I play a lot of billiards also. One of the things I learned from one of the great pool players is when you make a mistake just laugh it off. Efren reyes misses an easy shot or does something stupid laughs, scratches his head and then sits down and it is done. I still haven't learned to apply that at the chess board(or really the pool table for that matter) but it is something to strive for.
Although I think those of us that have a deep seeded hatred of losing do have an advantage in terms of getting better. It motivates you that much more to put in the work you need to do


. When you're enjoying chess and thinking completely objectively, with no nonsense clogging your mind, you play really well, so I'm now always trying to get in that state of mind to consistently play good chess.
. I rarely smile when I win, I'm just mildly excited).
I guess this was bound to end up in a place, considering how helpful and insightful so many people have been in this thread, that it would end up turning to the psychology behind the problem. Ultimately, that IS the problem, but it's also very obvious to me that the psychology behind the "enjoyment" and "overly-competitive" and "trouble handling losing" factors are common problems too, and not just with someone who's bi-polar. It's the bi-polar that makes it a much more life-disrupting issue.
So many of the suggestions made here will help others, not just Mark. I know he appreciates them, and I most certainly do. This is WONderful to have such support and people caring enough to put out there possible suggestions that could help. He posted a few more details than I expected or was necessary, but I guess the mood had him expressing more and honestly---it's not offensive and if it helped, it's fine with me since it's fine with him. The specific things that affect each person's life that create problems such as being overly competitive, etc. are what each individual needs to work out, BUT the general suggestions offered here are just that----general in a way that others can also benefit by them. This became a thread worth reading, I think, rather than the kind that has little or no value.
Thank you again, to all who've offered caring and useful suggestions!