There is also a belief that cannabis can prompt schizophrenia in those people who are genetically predisposed to the condition. Henry is open about the fact that he smoked a lot of the drug between the ages of 14 and 19 and his father believes this may have played a part.
Patrick confesses that when Henry became ill he was ?astonishingly ignorant? about schizophrenia. ?I soon learnt it is to mental health what cancer is to physical ailments,? he says.
The condition varies hugely from patient to patient. the symptoms include delusions, hallucinations and paranoia and are largely controlled by antipsychotic drugs. yet in common with a lot of people with schizophrenia, Henry refused to take medication because he believed there was nothing wrong with him.
?As far as he was concerned he was having some sort of spiritual awakening, which was at times exhilarating and at times terrifying but magical all the same,? says Patrick. ?He just couldn?t see that he was ill at all.?
Patrick and Jan were told Henry could make a good recovery if he only had one psychotic breakdown. so when he left the Priory after two months and resumed his studies they hoped they could put the episode behind them.
However, a year after Henry?s diagnosis, Jan had to make the difficult decision to have him sectioned after he was found naked in a friend?s garden. This time he was admitted to an NHS hospital.
Henry was to spend the next seven years in various institutions but he still refused to take medication and there was little notable improvement in his condition.
It was an agonising time for Patrick, Jan and Henry?s younger brother Alex. especially as Henry deeply resented being locked up and ran away about 30 times, sometimes disappearing for days on end.
On one occasion, a couple discovered him sitting naked in a snowdrift. he was suffering from hypothermia and frostbite and couldn?t remember his name. They took Henry to their home, kept him warm and called an ambulance.
?In general people have been incredibly kind and understanding,? says Patrick. ?We?ve never felt stigmatised and our families have been very supportive.?
Nevertheless, he says misconceptions persist about schizophrenia, with many people believing sufferers are dangerous and violent. the truth is 60 per cent of male schizophrenic patients attempt suicide at least once. Henry himself has lost friends to the illness. he admits he often felt scared when he was in danger, but was unable to resist the call of his visions and hallucinations.
Another assumption, Patrick adds, is that sanity and madness are two absolute states. yet even at his worst Henry was capable of lucid conversations and could be engaging and creative.
However his illness meant he could never fully appreciate the terrible pressure his behaviour put his family under. he still doesn?t seem entirely convinced that he is ill.
N ow 29, Henry lives in a halfway house in Lewisham, south London, and takes a cocktail of antipsychotic drugs, including Clozaril, which causes extreme drowsiness and a surge in appetite. he struggles to wake up in the morning and has put on weight.
In spite of these side effects his medication helps him to resist the voices in his head.
Henry will never be cured but his condition has improved to the extent that he and Patrick have co-written a book about their personal experiences of schizophrenia. ?We wanted to dispel some of the myths and give people a first-hand insight into psychosis,? explains Patrick.Henry writes beautifully about his visions and at times there is a sense of euphoria as he describes how at the height of his illness he talked to trees and saw sublime messages in spider?s webs and snowflakes.
?In some ways I didn?t want to lose the visions and the voices,? says Henry. ?People kept telling me I was ill but I just thought I saw the world in a different way.?
Even with medication Henry still struggles to tell what is real. he also continues to suffer from terrifying bouts of paranoia, believing strangers can read his thoughts. ?I call them my ?polka dot days?, as wherever I look I can just see rings. It?s so frightening I have to lie down and block it out.?
Next month Henry is moving to supported housing and will have the kind of freedom he has relished for so long.
Patrick and Jan hope with time that schizophrenia will dominate their son?s life less and less. For now, they are just thankful. ?In spite of everything, Henry is still here,? says Patrick, smiling fondly at his son. ?Not everyone is so lucky.?
l to order Henry?s Demons by Patrick and Henry Cockburn (Simon & Schuster, ?16.99) with free UK delivery, call 0871 988 8367 (10p/min from BT landlines) with your card details, send a cheque payable to Express Bookshop to Express Bookshop, PO Box 200, Falmouth TR11 4WJ or order via expressbookshop.co.uk
l to contact the mental health charity Sane, visit sane.org.uk