Henry's schizophrenia was diagnosed in 2002
Henry Cockburn and his father Patrick, a former war correspondent from Canterbury, have been talking about Henry's use of cannabis and his subsequent schizophrenia.
Patrick Cockburn and Henry have written the book, Henry's Demons, about how Henry and the rest of the family dealt with his condition.
In early 2002, Henry was rescued from the estuary at Newhaven. He had swum in it fully clothed and almost died of hypothermia.
He had previously been detained by police after attempting to jump off a bridge in Brighton.
"I thought I was special"
Henry described how he also talked to trees and had visions of Buddha in the sky.
Henry said: "I thought I was special and I got to see a side of the world that lots of people don't see."
"I saw my schizophrenia more as an awakening. It was when I gave up tobacco and marijuana that I started having these experiences."
Patrick said that the level understanding of what is going on in the brains of people with mental illness is comparable with what was known about physical illness about 100 years ago.
Cannabis and schizophrenia
The link between schizophrenia and the use of cannabis, especially at a young age, is argued by many scientists and psychologists, although scientific proof is difficult to obtain.
Marjorie Wallace is the Chief Executive of the mental health charity, SANE.
She said: "We are very concerned with the link between cannabis and mental health problems."
"The problem with the links between cannabis and mental illness is that there has been no proven cause. What we do know is that it can trigger psychotic symptoms...and those experiences may carry on and they may have repeated incidents and develop a long lasting illness such as schizophrenia.
Patrick Cockburn was in Afghanistan when he heard his son was ill
"We don't know who is vulnerable and who isn't. It's a bit like playing Russian roulette."
Henry does not see the link between smoking weed and skunk and his schizophrenia but he said that smoking cannabis is not a good thing. "You don't grow up, you stay the same age".
"What is really important is that people who do take it know that there is a chance that they may have this total mental breakdown." said Patrick.
"I enjoy writing"
Henry said that his life seems to be on an even keel since writing the book.
"It's been nourishing, and I enjoy writing. It's an opportunity I didn't take likely, and I'm glad I got the opportunity", he said.
"I hope that my story aids people, that it gives people a different angle on mental illness. A lot of people don't know anything about mental illness, and a lot of people feel forgotten."
Patrick said: "It would be good thing if people understood what happens with schizophrenia. You can get through it, and I think we have, so far."