Yeah Sad news.
Yesterday i was watching one of his movies "The Angriest man in Brooklyn", weird...
I think you can easily be bipolar beeing an actor, i mean if you're good at your job
you give 100% of yourself playing, so i think you can easily be caught in the middle and not knowing who you are
really at the end, especially if you act a lot i guess..., can play tricks on your mind after a while + the stress of "feeling" and "beeing" popular etc...
Wasn't it Jack Nicholson that was stuck in craziness a couple of months after playing in "One Flew Over the Cuckoo's Nest" ??
EDIT: Found this, and it was mainly rumors for Jack Nicholson, but it can easily be true:
http://www.businessinsider.com/actors-who-refuse-to-break-character-2013-2?op=1
Anyway,
RIP
...