lol
Basically, a 9BI downswing is nothing strange OP... Sure it sucks, especially the first time it happens. But you better get used to it
One way to look at it is that apparently you're not yet (mentally) ready for 50NL. If a swing like this effects you so much, move down a bit where you're more comfortable and loosing a few BI doesn't upset you as much.
At a 100k hands break even stretch (with a few downswings in between, one of my favorits a 14BI downswing in 2k hands... ). It sucks but hey, it happens (and I've seen a LOT worse).
Just don't make it influence your play, and if it does then quit for a while or move down where it doesn't hurt your bankroll as much.