Former Guantánamo detainee Shaker Aamer, now back in the UK receiving treatment in hospital, is being urged to adopt a low profile and allow himself a chance to recover as he begins what are expected to be years of rehabilitation.

Aamer, who has been reunited with his wife Zin, was due to meet his children this weekend, including youngest son Faris, who was born on the same day Aamer arrived at Guantánamo.

Trauma experts, former hostages and medical testimony provided by his psychiatrist, suggest Aamer, 46, faces a long and difficult battle to overcome the mental and physical afflictions caused by his near 14-year incarceration.

In a petition filed last year, Aamer’s lawyers said he was suffering a range of chronic health problems, the worst of which was post-traumatic stress disorder.

Dr Emily Keram, a forensic psychiatrist, said: “Mr Aamer experiences prolonged psychological distress and physiologic reactivity on exposure to reminders of trauma. He feels irritable, sad, angry, hopeless, and helpless on exposure to these reminders.

“He was visibly agitated when discussing traumatic material. Mr Aamer is fearful of using the toilet. Because the opportunity to do so was routinely withheld from him during interrogations, he associates his ongoing painful urinary retention, constipation, and efforts to relieve himself with memories of being interrogated.”

Keram also noted that Aamer had angry outbursts, which he was trying to better control and “feels guilty about not parenting” his children. “He experiences chronic initial, middle, and terminal insomnia. He [has] impaired concentration and memory, hyper-vigilance, and exaggerated startle response.” Many of his problems were caused by a severe lack of stimulation, triggering a condition known as special-housing unit syndrome.

According to experts, symptoms worsened when Aamer was held in isolation and improved when he was allowed interaction with other detainees. According to Keram, manifestations of the syndrome include “profound dysphoria, increased anxiety, and auditory hallucinations.”

Terry Waite urged Aamer to withdraw from public view Photograph: Murdo Macleod/The Guardian

Former hostage Terry Waite, who was held captive for 1,760 days after going to Beirut in 1987, urged Aamer to withdraw from public view for a while to give him the best chance of recuperating. “He has suffered a grave injustice,” Waite said. “Whatever the background, to keep someone for 13 years without charge is really beyond the pale. The best thing is for him to withdraw for a while to get the treatment that’s necessary.”

Some of Aamer’s fellow detainees still suffer as a result of their detention years after they were released. Omar Deghayes, a Libyan-born British resident released in 2007, is blind in one eye as a result of his treatment by guards. Jamil el Banna was said by his lawyers to have suffered from post-traumatic stress syndrome, severe depression and suicidal tendencies. Some detainees have tried to reinvent themselves, to break free from their past. Binyam Mohamed, who arrived back in the UK in 2009, is said to have changed his appearance.

Experts say it is not possible to predict how long Aamer will need specialist counselling. Keram said: “In my experience and based on the medical literature, PTSD patients with presentations similar to Mr Aamer require years of medication treatment and often require life-long medication administration. With respect to psychotherapy, PTSD is most effectively treated by a combination of cognitive behavioural therapy, skills-based therapies, and supportive psychotherapy. If the patient has a family, marital and family therapy is also required.”

Phillip Hodson, a psychotherapist and patron of the West London Centre for Counselling, said that much would depend on “the steel in the man” during his time in captivity. “Optimists live longer,” Hodson said. “Having a belief that the sentence will end is important. Having inner resources can be crucial.”

Here, Aamer’s strong religious convictions may have helped sustain him in his most difficult times. “Religion does provide a structure for survival in these circumstances,” Hodson said, noting how a strong sense of patriotism helped some US veterans survive being held by the Viet Cong during the Vietnam war: “I talked to Terry Waite about this,” Hodson said. “His belief in God, although tried to the limit, was an asset to him. Religion has its uses.”

Shaker Aamer’s plane arrives at Biggin Hill. Photograph: Keith Larby/Demotix/Corbis

Aamer’s lawyers have signalled that he wants to set up a peace foundation, to ensure others do not go through similar experiences. Hodson said this could be a fruitful venture. “He needs to try and make sense of all that has happened. You could be very depressed because your life has been stolen from you, but if you can work to prevent this happening to others, or if it does happen to others, give them some means of getting through it, give it some meaning, then you are creating some kind of monument. We are emotional creatures, we need rituals and symbols. Why do we have poppies? Because people gave their lives. It must not have been in vain.”

One immediate challenge will be how Aamer engages with his four children – the youngest of whom he has never met. While the reunion will have been something Aamer must have spent years contemplating, Hodson said there was a need to be realistic about expectations.

“You are a stranger and you return and, while they welcome your return, it will cause a lot of grief. Don’t expect what you imagine to be a joyous reunion to be a bundle of fun. It has got its dark side and its drawbacks. Nothing is wholly good. Things are always mixed. Each family is a secret unto itself.”