“Among the creative professions, it’s very, very common,” says comedy producer and performer John Lloyd, who made the TV series QI and Blackadder.

“There’s a very, very high incidence of bipolar disorder. It’s because stable people think the world’s fine as it is. They don’t see any particular need to change it.

"Creative people don’t feel like that. People who want to change the world tend to suffer a lot for it.”