Very sad. He was a rather dark dude his whole life, recovering from heroin addiction that brought him down pretty hard. In a New Yorker profile a few years ago, he commented something along the lines of "I travel constantly because I feel like if I don't, something is going to catch up with me and I won't know what to do."
Seems kind of common with these high-energy, full-of-life entertainers that appear to have everything going for them. A lot of that is a mask, especially with recovering addicts. Think Chris Farley, Robin Williams, et al.