By Dominic Casciani
BBC News Online community affairs reporter
How does someone deal with being tortured?
Moazzam Begg's family has campaigned for his release
On Friday lawyers for British Guantanamo Bay detainee Moazzam Begg said his first uncensored letter to reach them showed he had been tortured during his two and a half years of detention.
But while his family and legal team fight for his release, Mr Begg may face a difficult and long recovery, warn experts.
Clive Stafford-Smith, Mr Begg's US counsel, said his client was being held in solitary confinement. The cell was partitioned by an opaque wall with a camera constantly monitoring the room.
Mr Stafford-Smith said the partitioned cell had been designed to allow interrogation of the prisoner without needing to remove him. This in turn, he argued, compounded the sense of isolation.
But what effect does this have on the detainee?
The Medical Foundation for the Care of Victims of Torture is the only professional medical body in the UK which deals exclusively with torture victims.
Dr William Hopkins, a consultant psychiatrist, is among the doctors who see some 3,000 patients at year at the foundation.
Dr Hopkins said many of his patients had been held in solitary confinement or subjected to sexual humiliation, particularly in Iran, and that the effects were very grave.
"Someone who has been held in solitary confinement can show signs of depression, anxiety, mood swings, feelings of helplessness and suicidal thoughts," he said.
"There can be paranoia and disorientation which then leads to a loss of sense of identity."
As they struggle to comprehend what is happening, says Dr Hopkins, the detainee begins to lose a rational understanding of both surroundings and time. In the worst cases, they begin to hallucinate.
Interrogators and torturers seek to maximise the detainee's vulnerability under such conditions, says Dr Hopkins.
In one example from World War II, British interrogators would dangle devil figurines before German prisoners in solitary confinement, the idea being that it would confuse, disorientate and make questioning easier.
Dr Hopkins has seen victims of solitary confinement suffer from acute pain caused by sensory deprivation.
"Solitary confinement cells can be terribly quiet," he said. "If someone then comes along and simply bangs a door, it can be very frightening.
"Guards use these kinds of techniques all the time to psychologically torture people. They may shout at someone - and if you have not heard anything, it can be very painful.
"But perception of sounds can also alter. A running tap can be perceived as a voice. And of course they are going to define it in a persecuting way because of the vulnerable state they are in."
But the suffering does not end on release. Former detainees can suffer shock, guilt, shame and a sense of powerlessness.
Dr Hopkins said: "When someone is tortured, they don't have time to feel things properly, they are just trying to survive. It's only afterwards that they get in touch with their feelings.
"In many cases the experiences mean they have lost a sense of who they are, where they were going [in life]. This creates apathy and depression.
"If there has been sexual abuse, then there can be great feelings of shame, particularly among the Muslim patients I have seen. Some of the men I have treated believe [the rape] has turned them into women."
Dr Hopkins said that with significant professional help, some people could do "reasonably well".
"But people in this situation need extensive medical treatment, sometimes at least once a week for several months."
One of the controversies surrounding Guantanamo Bay is the nature of the medical care. The US government insists all detainees receive appropriate medical treatment, if they need it.
But campaigners suggest that doctors who work for the US military have become complicit in the controversial nature of the detention.
There are claims that military doctors witnessed torture during interrogations at Baghdad's Abu Ghraib prison. The US says there is no evidence for these claims and insists military doctors have a humanitarian role.
But Dr Asif Chaudry, of charity Doctors Worldwide, called on the US government to allow immediate access to Guantanamo detainees.
"It's important independent doctors see the people in Guantanamo Bay. The sense I get is that a lot of the doctors working for the US military are complicit in torture.
"If possible, these doctors should be Muslims, particularly any psychiatrists who go because of their understanding of what might be now going on inside the minds of these men."