Sir Pawn, the answer lies in the comparison between win rate and standard deviation. Most of the standard deviations I've seen in my own analyses of my game are about 40 - 50 ptBB/100. Basically, w/ win rates around 10 ptBB/100, you have nearly 80% winning sessions, so the downswings are pretty rare. When you get down to 3 - 4 ptBB/100 win rates, you have more 5 - 10 BI downswings possible. And of course, at 2 or less ptBB/100, you have tons of 10+ BI downswings because only about 55 - 60% of your sessions are winning ones.

That's the math side of things. Someone else could give you more practical advice. I just know that good players all over FTR have experienced multiple BI downswings - like 30+ BI's in some cases, while playing decent poker.