I once caught a glimpse of my medical records moving from trolley to receptionist’s desk at the GP. Perhaps they have long been computerised, but then they were housed in a large, weary-looking file. They had the heft of a first draft of a novel, a comprehensive and messy catalogue of pains and breaks, results and dead ends and cures. They were nothing unusual for a woman my age. One thing not in there, though, was any reference to or diagnosis of the dominant ill of our time: depression. Nor anxiety, insomnia, or any mental struggle whatsoever. No antidepressant has passed my lips; I have troubled only one counsellor briefly – when my father died.

However, I know for sure that, after the birth of my daughter and for a few years after, I was not in the world as I knew it previously.

I occupied an alternative reality, one that encompassed me and my baby and made sense of the onslaught that new motherhood brings. I was, in the words of a friend, “stark staring bonkers”. But I got up in the night as required, fed and cared for my baby, and attended all required groups, classes and appointments. I remained married and held down a job. My baby was healthy and seemed unaware that her mother was not mentally present in the ways society demands.

No one noticed that I had vacated the space I once occupied, and I know now that, as long as you don’t actually drop and break your baby, no one cares at all about your behaviour.

I am probably fairly typical of my generation of women: I married quite late and started a family late. I had had a lot of years of being an individual. I had all sorts of notions about independence: I thought my ability to think independently and solve problems was my primary asset. Combine this with a profound ignorance of children and babies and, indeed, most aspects of a woman’s traditional role, and it is plain I was ill-prepared for what awaited me.

I wanted my baby more than anything in the world. I loved her before she was even conceived. I longed for a family and wanted to have responsibilities and duties: these give life its meaning. I wasn’t a reluctant mother at all. But I had no notion of being simply a vessel: I stubbornly continued to think that, as an individual, I still mattered. What a vision I must have presented to the steady stream of officials who began to enter my life when I was pregnant: determined, articulate and believing myself the leader of the burgeoning team of two. Perhaps it was no surprise that other pregnant women grew scolding and told me to throw away my books, and from now on avoid any pleasure I had previously enjoyed for the sake of my baby.

I had a dangerously well-developed sense of self. It is this basic identity that new motherhood would destroy.

Polly Clark at home on Scotland’s west coast. Photograph: Murdo Macleod/The Guardian

Unlike every other woman I know who gave birth around then, I had what the doctor called “the experience we hope for everyone”. My baby was premature, which meant an emergency, and so the NHS pulled out all the stops: in the room at the moment of birth were a consultant paediatrician, an obstetrician and two midwives. One of the strongest memories I have is of the consultant paediatrician painstakingly explaining everything to me and checking I understood, even as I was writhing half naked and unable to form a coherent sentence.

He treated me as a person, even though I did not look like one at that moment. Mostly women are left alone for long periods and give birth without anything like that amount of skilled attention. But, although that doctor’s kindness is a standout moment in my experience of birth, nothing, not even a full complement of caring staff and being treated with dignity, can change the hard fact that birth is painful and frightening, a facing of one’s mortality and a loss of innocence akin to an experience of war. Most women will have not come so close to understanding death before that moment. It is a profound shock, and no less shocking for being an everyday occurrence.

I re-entered the world of the maternity ward, and the pressure began – to leave the hospital to make room (no seven to 10 days of lying-in these days) and to breastfeed on demand. There was no recognition of the enormity of the experience that had just occurred. It’s my belief that many women after birth have post-traumatic stress disorder: instead of being offered rest and help, they are sent home to be perfect mothers on no sleep.

Part of being a perfect mother in those early days is breastfeeding on demand. This did not feel like an “option”, it was official guidance, and to defy it set you against all the community health professionals who visited your home in the days and weeks after birth. My own baby was too premature to breastfeed. This did not prevent the midwives trying to make me, and questioning my commitment to my baby when I stayed on the feeding routine when I brought her home.

Having cyclical disagreements about the same thing when you are vulnerable and exhausted makes you doubt your own mind like nothing else. I had no family nearby to offer help, and experienced this period as a time without kindness, where everyone seemed to view me as an obstacle to the fulfilment of their own aims regarding my child.

Nevertheless, while in the fog of those early months, I knew enough not to admit I was struggling to cope. Every new mother knows that when the midwife comes round looking for signs of postnatal depression, you don’t answer honestly. In these days of anonymous reporting to social services and general paranoia about child welfare, any admission that you may not be coping could lead to your child being taken from you. For, as my friend summarised pithily, everything is now both your fault and your responsibility, and all of it must be achieved perfectly on levels of sleep that would normally be considered a torture weapon.

My baby is now 10. My medical records are thicker, but still they have no reference to any problems with my mental state. Almost to a woman, my friends will nod enthusiastically and agree they too were “not themselves” for months or years. Some of us will have flirted with drinking too much, or self-medicating in other ways; others of us may simply have been in a very bad mood, enjoying nothing about our lives for a long time.

Though we are, for the most part, no longer at odds with reality, I would posit that we are all profoundly changed by the experience. My identity as a person before motherhood has been obliterated. I have glimpsed that other country, that scary Handmaid’s Tale one, where women are nothing but vessels and slaves. I have experienced unkindness of the sort only doled out to third-class citizens. I may be a lucky mother of a happy child, but I have glimpsed what lies beneath our civilised veneer and it frightened me enough to be a factor in stopping at one child.

As one mother told me, it is the ones who don’t go mad who are weird. For when the world as you know it has vanished, is it really madness to try to escape? I “checked out” in some profound way, became instead a machine for caring, with a beady focus on detail. It’s a survival tactic employed by the kidnapped, the incarcerated. Do not reflect on what you have lost. The loss is so great and sudden it cannot be properly comprehended. Find a way to exist through time, to keep the time passing, to fulfil the obligations. Your mind, your soul, they can go where they will, and something of them will return. Just don’t drop your baby.

• Larchfield by Polly Clark (riverrun, £14.99). To order a copy for £11.24, go to bookshop.theguardian.com or call the Guardian Bookshop on 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.