My bankroll is 300 buy ins for the games I play. However after the last two days I'm down to 250 buy ins. Probably the worst run I have ever had. The last beat I had A,A preflop with 5 buy ins on the table from winning. Villain is stacked well too, Villain reraises me half my stack, I shove. A,A vs K,10suited, board came out 6,7,8,9,5. I normally don't feel bad about losses, but that one hit real hard after two days of losing. I am hoping this is more common than I think, I love poker, but right now the desire to play is diminishing.
You may need to adjust your perception of buyins. If you're playing 500BB's deep on a regular basis you should think of your bankroll has being half of what it really is.