I remember an article by Mike Caro about running bad. He said even when he's running bad he tells everyone at his table he's running really good. Partly so they all think he's going to win, and they expect it, partly so that he keeps a good attitude. I know when I run bad it tends to be because of my attitude. It starts with one bad play, I beat myself up about it, then I'm gone for at least the rest of the night.

Just my personal experience... I don't play online enough to have any statistics to back it up tho.