Is mental illness real?

A lot of the time I believe I have at least one, probably more, mental illnesses but then I start to question whther mental illnesses are real. I'm not suggesting that the way people feel isn''t real but that maybe people with 'disorders' subconciously choose to be that way. I feel as though I've clearly made every decision that's led to where I am so if I'm crazy, I've done it to myself and this would logically mean that I'm the one with the power to undo it. I don't know, I think I'm just feeling confused and would like to hear people ideas on this. Please don;t just respond with 'of course they're real because I have blah blah and it feels like blah blah blah' I'm aware of this view point, I'm more interested in your ideas and theories rather than personal tales of woe (by all means, include them if they are relevant though). Cheers