So I'm writing a book where my main character is clinically diagnosed as being catatonicly depressed. If I write it without therapy will I become depressed? I've heard that sometimes those kinds of things happen to authors and they get 'stuck in' their characters lives.
I'm no psychologist but think you'd need some predisposition for this to happen. Bits of you come out in characters, IMO, so maybe a few authors write too close to themselves. And perhaps they write first person, which makes it worse.
But it's very easy for stress-related illness to creep up while you're not looking. Is the character's situation something you've experienced, even secondhand in some way, or just intrigued about? I'd examine why you feel you have to write about it before you start and make sure you're happy with your reasons.
Let's be careful out there :)