There is a very old joke; it has appeared in different forms over the years, most famously in Alan Moore's seminal graphic novel Watchmen. Most retellings add or change elements, but the basic structure and punchline remains the same.
A man goes to the doctors, and says,
"I need help, I'm feeling utterly depressed and life seems not worth living."
The doctor pauses for a moment and says,
"We should be able to treat that very simply. There is a great comic, Pagliacci, in town tonight. Go see his show, and you should feel much better."
The man starts weeping hysterically,
"But Doctor," he says "I am Pagliacci."
Obviously we know now that clinical depression is not treated by seeing a good stand up. However, the age of this joke implies there has been a long standing, quiet acknowledgement between the mentally ill and depressed with comedy.
Many of the most popular stand up comics or comedy performers of all time battled some major inner demons. People like:
Richard Prior, Robin Williams, Stephen Fry, Tony Hancock, John Cleese, Spike Milligan, Peter Sellers, Dudley Moore, Jim Carrey, Joan Rivers, Ben Stiller, and many others are all known to have suffered, or suffer, either from depression or bipolar disorder (notably, Stephen Fry, who has documented his experiences with it extensively). These are people who virtually gave their lives to the pursuit of making others laugh, but everyone mentioned above live, or lived with, such intense pain.
It seems almost impossible that someone like Robin Williams, someone who for decades brought joy to millions would live in a state of such anguish that the mere thought of suicide was even present, let alone acted on. He should have lived as happily as he made people. But he didn't. His suicide is a tragedy beyond thought really, that someone of such unique talent could be capable of that. But all suicides are tragedies beyond thought. In the year that Robin Williams took his own life, there were over 40,000 suicides in the USA alone, and 90% of suicides occur in people with mental illness.
There is always a danger of falling back on that old cliche of the tortured genius/artist. Dangerous, because it might suggest that treating mental health might stifle creativity but there does appear to be a curious link between comedy and mental health. But why is this?
In a 2014 study (Ando, Clarige, Clark. Psychotic Traits in Comedians, 2014) by the University of Oxford, researchers found, in a pool of 500 comedians and 350 actors, that these creative performers showed an unexpectedly high number of psychotic traits, similar to those found in bipolar disorder or schizophrenia.
The comedians studied, in particular, demonstrated high rates of both introverted anhedonia (the inability to feel pleasure) and extroverted impulsiveness. Though it's often been found that those suffering with schizophrenia find it difficult to understand comedy, in less severe forms, the "overinclusive thinking" commonplace in psychotic thought patterns where ideas and thoughts connect in illogical ways can be useful to think creatively as it allows a great ability to connect strange and unexpected things, which is common in comedy.
One theory why comedy is the avenue for so many mentally ill people, is that it provides an avenue for some kind of therapy. Causing a room full of people to laugh can create a break from all the misery, and perhaps bring in a sense of worth. Perhaps gaining the attention from performing on stage is a reprieve from the intense isolation of such conditions. Indeed, there is an organisation in the US, Stand Up to Mental Illness lead by counsellor and comic, David Granirer, which looks to involve those with mental illnesses in comedy to open up about their issues.
However, there is an alternative view. One that is troubling, but bears noting. Mental illness is far, far from exclusive to comics or performing talent, and there are a great number of acclaimed performers without mental illnesses, (or, at least, are known to have a mental illness). But consider the fact that one in four of the population suffer from mental illness in any given year. It could be the case then that, despite what is suggested in the report mentioned above, that the high numbers of mentally ill people who perform, could be emblematic of the population as a whole.
Only when someone is on stage actively talking about it, does their relation to mental illness become reorganised publicly, whereas many members of the audience suffer similarly but don't speak about it.
In a sense, attention is drawn to the trials of a particular individual, not the many.
In either case, numbers of people who suffer mental illness are vast, too vast to accurately number.
Their battles and problems are often unspoken and unknown; they may have trouble truly speaking honestly about it whereas the comedian may not, so although it might seem, from a distance, that that when someone openly speaks about their condition they are exclusive to it. They are not, but when they do speak out, that great wall of social stigma, is chipped away, bit by bit.