Man down … visiting a wounded soldier, Sapper Michael Clark, in Afghanistan in 2010. Credit:Courtesy of Defence Media Released from responsibility, it is as though a dam in my mind has cracked, flooding me with despair. The barriers I built and shored up over the years, especially over the past 12 months, start to shift and buckle, releasing a pent-up misery. The sadness and regret that I had pushed deep down inside resurface, amplified. Memories flood my mind: cold bodies in a morgue, torsos violated by bullets or explosives or a shattered helicopter; the pain and uncertainty of the wounded whose lives have been forever changed; the horror in the eyes of men who have picked up pieces of their mates. My nights are tormented by ghastly nightmares, punctuated by sudden shouts as I come awake, shaking and confused. The melancholy that has lurked in my heart begins to tear at my sanity. I try to fight it. Surely I can beat this by force of will. I deliver myself a stern lecture: Snap out of it! You're whole, unharmed, alive! What have you got to moan about? I force myself to think of the hurt being suffered, right now, by men who have survived awful wounds. I think of the wives and partners making daily treks to hospitals, sitting in sterile rooms, listening to doctors' reports, supporting their damaged men. I force myself to think of the grieving families of the dead. My wife, Jane, has endured a long separation and months of worry, and now here I am moping about like a sulking child. I am dismayed by my weakness and selfishness. You pathetic jerk! Get a grip on yourself! Determined to be "normal", I smile at small jokes or amusing stories, but it feels false, skin-deep. I try to take an interest in the lives of friends and family, to share in their achievements and concerns, but inside I'm a dark pool of sorrow. I feel constantly distracted, as though events around me are ethereal - the weight of memory and the millstone of guilt seem to be the only things of substance.

Guiding light … Cantwell with his wife, Jane, earlier this month. I talk to Jane, my one true confidante, and she encourages me to stop being so hard on myself, to remember the happy moments, the enjoyment of being with servicemen and women, the pride in them I had spoken of so often. This sound advice bounces off me. An undirected anger works within me. I am angry about the random violence that claims lives on the battlefield. I burn with anger at the months and years of pain confronting the badly wounded. I resent the fact that they must now struggle to live without eyes or legs. I am angry with myself - I should have done more, thought of some new technique, insisted on some new strategy, to save them. But I didn't. I couldn't. I was powerless, a spectator in a deadly circus, cast in the role of official mourner and speech maker. The rawness of the new memories sharpens images from the past. The old familiar demons invade my sleep and sometimes my waking hours. I see the hand of a man buried alive in Iraq. The thump and buzz of incoming artillery fire fill my ears. I am seized by the terror of leading soldiers across a dark, empty desert. My fingers feel the weight of a man's head and I smell the stench of burnt flesh. The dread of death, so close, so immediate, hollows my chest, as it did when I forced shaking legs to walk past half-hidden mines. I am transported back to a Baghdad suburb where a car bomb in a marketplace left a little girl's pink sandals floating in a pool of blood. I taste bile in my throat at the realisation that I have ordered men down a road that killed them. I feel like I'm losing it. In the midst of this misery, I am summoned to Canberra to see Lieutenant General Mark Evans. He wants me to debrief him and his senior staff on my observations and assessment of the Afghanistan campaign. It requires an effort of will to make the trip and present myself. I play the role of a calm, rational returned general, offering wise comments and penetrating insights to him and the other officers. I even make a few jokes. Inside, I'm churning.

Afterwards, Evans, always a gentleman, walks with me to my vehicle. In the car park he asks me how I am, really. He has detected my unease. My instinct is to trot out another glib answer, to say that I'm fine. But I'm not fine and I'm tired of the facade. I take a deep breath and tell the truth. I say that I'm not well, and that I'm troubled by the losses of the previous year and older memories. I tell him I am having trouble sleeping, that I feel unhappy and guilty. He tells me, rightly, that war is always a source of sadness and loss, that lives spent on the battlefield are the brutal currency of combat. I know this but my mind rejects his counsel. I ask him to speak to Angus Houston, the Chief of the Defence Force, and tell him about our talk. When I get back to Puckapunyal, I know that I must do something to seek help or go under in a wave of misery. I go to the base's medical centre and the office of a military psychologist. It is the start of an awful, belittling, painful but necessary journey. I am now officially mentally unwell. The psychiatrist at Melbourne's Repatriation Hospital is attentive, understanding and very familiar with the emotional trauma that can arise from military service. He tells me he believes I am suffering acute post-traumatic stress disorder (PTSD) and depression. He says medication will help and that he will arrange a program of meetings with a psychologist, along with periodic sessions with himself. I walk out with a prescription for drugs to calm my anxiety and rebalance my moods and an appointment for some counselling. I still feel wretched, but at least I'm doing something about it. When Houston calls in May 2011, I have begun the course of medication. I have also made up my mind that I cannot continue to serve in the army. The prospect of being selected to be the Chief of Army is an extraordinary one, especially for someone who started life in the army as a private. It would be a career-topping pinnacle. It is also impossible. Even if I were to be chosen, which I doubted, I would not be well enough to do the job.

I tell Houston straight up that I'm not fit to command, and that I should be considered unavailable for the army's top job. In his quiet, unhurried way, Houston says, "John, you will not be Chief of Army." It's a mercy: the game is over. Now I know where I stand. With this behind me, my hope is I can get better. I could not be more wrong. Sorrow now takes centre stage in my mind. Irrational anger simmers, bursting out at the slightest provocation. I seethe at the indifference of most Australians to the efforts of our troops overseas. Anxiety stalks me. At shopping centres, I feel threatened, surrounded by unseen dangers. I find myself moving towards the walls of crowded spaces to protect my back. I look for exits and places to take cover. The hyper-awareness that had me flinching at unexpected noises now becomes a disabling compulsion - I jump at any sudden noise. One day we are on a train to Melbourne and the conductor behind me calls out, "Tickets, please!" I jerk in terror, throwing up my arms defensively and emitting a cry of fear. Several people laugh. To my total humiliation, I start to weep. A battle is being waged between my rational intellect and my damaged mind. When the guilt reduces me to tears, or when the anger blinds me to the hurtful things I say, or when I convulse in fear at the slamming of a door, the real me - the thinking person who has led soldiers in battle and managed the most complex problems - watches aghast at the blubbering, twitching, confused fool I have become. I'm a mess. And my darling Jane bears the brunt of my despair. I add shame to the list of emotions swirling in my mind. I've become a person I despise. Compounding this is physical pain. The damaged vertebrae in my neck, the injury I sustained in a training accident on a tank back in 1982 and aggravated in Afghanistan, has deteriorated further. The pain is intense.

The combination of pills for depression, anxiety and pain relief leaves me dull-witted. I find myself groping for the right word or mangling my speech when I have always prided myself on my vocabulary and speaking skills. I drop glasses and plates. I sleepwalk and wake, confused, in an odd part of the house. When I do sleep, it is a visit to Hell. The nightmares have become more horrid, vivid and frightening, and they come every night. Then one day I fall off a cliff; at least that's how it feels. I am in the office of my psychiatrist and Jane is with me. On the way in, she whispers, "Be strong, darling." At one point the psychiatrist asks, without emphasis but watching me closely, if I have had thoughts of suicide. I recoil at the words, but the idea of oblivion, of ending all this, seems like an escape. I stammer, then it comes out: "Sometimes I wish I was dead." Then the tears come, from such a deep place that I can hardly breathe. The look on Jane's face pierces my heart. The doctor is concerned. He quietly suggests a period in hospital for more focused treatment. He wants to change my medication and increase the dosage, and hospital is the best place to do this. He suggests a week, perhaps a little longer. The next day I wave goodbye to Jane, who is in tears, through the wire-impregnated glass of a door in a psychiatric ward. I am locked in. When I find my way to my room, I sit and weep like a child. How did it come to this? What the hell am I doing here? Outside my window, just metres away, construction workers in hard hats and fluorescent vests are building a new wing for the hospital. They drop bundles of steel pipes onto concrete flooring and hammer on metal beams. Each crash evokes a convulsion of fear. I lie on my bed, waiting for the artillery shells, or the car bomb, or the improvised explosive device (IED). Restful it isn't. Over the days that follow, the change in my medication regimen goes well, although there is one bad day when the demons come crowding into my room with such ferocity that I press the button to summon the nurse, who finds me incoherent and sobbing. More pills are administered and I sleep for 12 hours. I spend most of my time alone, avoiding the other patients locked in the ward with me. My room has unusual fittings: the taps are buttons, the door handles are nubs, there are no towel racks, and the shower curtain rail is embedded in the ceiling - it's suicide proof. I feel out of place, but perhaps I'm kidding myself.

Late in my week-long imprisonment, I have a cathartic session with a senior psychiatrist, a professor, and for the first time ever I tell my story in full. I describe every event that has shocked or revolted or terrified me, one after another. It's a long session, and by the end I am a mess. I feel like I've been bashed. But I also feel like I've crossed a bridge, or at least taken the first steps onto it. That night I have only one nightmare instead of the usual series. The next day, I dress in my street clothes and put my pyjamas away in my small suitcase. I want to feel normal. I ask if I can go for a walk outside. After some deliberation, I'm allowed to join a small, supervised group of well-behaved patients on a short stroll around the block. On the last day of my stay, I am allowed to walk alone, unsupervised. I head for a cluster of shops down the road, in search of real coffee. I am almost there when I see rubbish on the footpath ahead of me, the wind whipping at a black plastic garbage bag. My mind screams, IED! I freeze, then force myself to calm down. You're in Melbourne, it's just a bag of rubbish. Keep walking. I stare at the flapping black bag. Take a step, you idiot! I take a step, then another. I keep my eyes on the bag until I am several paces beyond it. My pulse only slows when I drop into a seat at a coffee shop. It has been a year since my stay in the ward. I have retired from the Australian Army after 38 years of service. Jane and I vacated the last army married quarters we will ever occupy, moving to the Sunshine Coast. Our new home, the 23rd house we have occupied during our life together, is set among gardens and has a creek running through it: a quiet, restful sanctuary. I finally had surgery to relieve the chronic pain in my neck and left arm. Now I have only a little residual pain and a metal plate in my neck as a souvenir. I still suffer nightmares on most nights. At times I wake violently, thrashing about, fighting off ghosts. The pills help, although I still feel a bit groggy the next day.

I still can't drive a car except for the shortest of trips into the town near our house. I don't trust myself. I can be fine, but then a car will come from a side street or veer in front of me and I suffer a convulsion of fear. The words "car bomb" are on the edge of my mind. This happens when I'm a passenger, too, but at least then Jane is in control. Bizarrely, I can ride a motorcycle without having these foolish panic attacks. I have no idea why. Busy places are still difficult. I'm told it's because I feel I'm not in control of my surrounds. The noise is unsettling. The scream of a child will rasp my nerves like a rusty blade, while the crash of a shopping trolley causes me to spin, half-ducking in expectation of an attack. It's ridiculous, I know, but that's the way it is. From time to time I become deeply anxious, but can't say why. Sometimes I have an overwhelming desire to get away from where I am or to avoid an upcoming activity. Travelling to one of the rare social events I can tolerate, I occasionally become so tense that Jane can sense it in the car. I have a feeling of dread, even though I know the gathering will be pleasant and undemanding. I force myself to go through with it. I try hard not to dwell on the troubled past, but it invades my consciousness without prompting. At other times an insignificant reminder of a place or a person, or even a smell, will trigger a vivid memory. Sometimes it's the other way around: I have memories so strong I can smell the places where the original incident occurred. I smell strong perfume and burnt flesh whenever my mind takes me back to the bombed wreckage of cars north of Kuwait City. Mental images of the bombed market square in Baghdad are accompanied by the smell of raw sewage and blood. When I recall bodies in a mortuary, I catch a whiff of antiseptic and bodily fluids. My ability to concentrate has improved, although I sometimes forget simple things. Jane has to remind me to take my medication, even placing it in my hand. My sentences sometimes drift to a halt because I can't remember the word for something. At times I feel like a simpleton.

Sometimes I'm prone to overblown emotions and now cry easily. I have become a bit of a serial hugger; I hug my dad and my brothers and some of my male friends without the slightest hesitation, an activity I once reserved exclusively for women and girls. It feels good and right. Rationally, I know my feelings of guilt and remorse do nothing to ease the suffering of mourning families or the pain and disability of the wounded. Emotionally, though, I feel compelled to bear part of their burden. I constantly wear a braided wristband, one I made in Afghanistan from parachute cord. It is fastened by a button; the small click it makes whenever I place my hand on a desk or tabletop prompts me to spare a thought for the men killed under my command. Some might think this maudlin; I think of it as paying respect. I am determined not to wallow in my condition. I am fortunate beyond words: I have found and kept the love of my life, Jane, and we have raised two boys into men we are proud of; I have had an extraordinary career, filled with excitement and change; I have seen the world and met countless amazing people; I have had the thrill of command and the satisfaction of success; I have been humbled and uplifted by guileless young warriors; I have been trusted and have trusted others with my life; I have walked with heroes, and count them as friends; I have had adventures you can't pay for and rewards you can't buy. I would not change my career, but I know it's come at a cost. One day I might accept I am wounded, but the memory of the physically ruined men I once commanded is too raw to allow that yet. What I do know is this: I have been a soldier; I have served my country; I am proud of what I have accomplished; I have endured hardship, trauma, pain and loss; I have done so voluntarily; I am not a victim, I am a survivor. I understand that I am on a long journey of recovery, but I know also that I will complete that journey, someday. I am determined to get better. I will beat this thing.

Edited extract from Exit Wounds: One Australian's War on Terror by Major General John Cantwell (with Greg Bearup), published by MUP on October 1. Lead-in photograph by Tim Bauer. Like Good Weekend on Facebook and get regular updates on upcoming stories and events: facebook.com/GoodWeekendMagazine