My thought is you may not be following good enough bankroll management guidelines. I strongly recommend 30 buyins for whatever NL you are playing and then dropping when you hit 20 buyins at the level you're at, NOT 30 buyins for the level below. So, to even play $10 NL, you need $300 and from the original post, I infer that you were playing @ $229, if not sooner. Furthermore, you mention playing $5 NL with your current bankroll and I think you should be playing $2 NL and NOT $5 NL until you reach $150 and dropping down to $2 NL if you reach $100. So, it's doubly concerning that I infer by the title of this thread that you have been playing $10 NL the entire time, when you should have dropped to $5 NL when you dropped to $200.

It's hard to say why you jumped up so much and then down so fast, but it's possible you were just getting lucky with the wins and then when things evened out, it may have caught up and not being properly rolled just added more fuel to the fire for a faster fall. OR, maybe you're just unlucky on the downswing, but in any case, having the right bankroll for the right level is crucial to all of our success. No limit has a LOT of swings, both good ones and bad ones, and you have to have the bankroll to sustain them and also prove that you are actually beating the level you're at.

Good luck @ whatever level you play.