I think this is one area where the multitablers have an advantage over the single table players. Multitablers don't have time to dwell on bad results because there is always another hand on another table that requires their attention.
Depression from losses is a different issue. You can't win every time and losing streaks are part of the game. If losing depresses you because you can't afford the losses, you shouldn't be playing. If losing depresses you because it hurts your ego, get over it or stop playing.
Also, being afraid to lose makes it impossible to be a winner. There's a fantastic quote from the movie "Searching for Bobby Fischer" that I've never forgotten. It's a movie about child chess prodigy Josh Waitzkin. This quote is said to Josh by his street-smart Central-Park-playing chess buddy Vinnie (Laurence Fishburne) about Josh's chess coach Bruce (Ben Kingsley):
"He didn't teach you how to win, he taught you how not to lose. That's nothing to be proud of. You're playing not to lose, Josh. You've got to risk losing. You've got to risk everything. You've got to go to the edge of defeat. That's where you want to be, boy - on the edge of defeat."
All the above IMHO.