Yes, move to the low end. I've heard it's fine to put 10% in play, but not lose an entire 10%. If you had $600 @ $10NL, and lost 10% - that's 6 buy-ins. You should NOT be going through buy-ins that quickly. A full buy-in is a precious commodity in NL and if you don't have a DEEP bankroll (like 60 or more), you can't afford to lose too many and definitely not in one day.

If you've always played 6 max, then maybe you should stay there. My logic for suggesting full ring is that it's a bit easier by design. You and villains should play a more narrow range of hands and thus hands become more well defined and there's not a lot of pressure to pick up pots since the blinds don't come around often. You'll win less pots, but bigger pots. Decisions should be easier. At 6 max, you're constantly making decisions and having to push small edges and marginal spots. I wouldn't say to AVOID this, but just know if you're struggling, starting out, trying to move up in stakes, or whatever, full ring can help you get your bearings better than 6 max. If you've always been @ 6 max and want to stay there, you should probably stay put, but @ $5NL. And just keep in mind that fewer players usually means higher swings and more challenging play. Make sure you're mentally prepared for it.

It's probably hard for anyone to give more specific advice since you've just posted your session results, results graphs, and BB/100. Instead of numeric results, you should post some interesting hands to discuss - both ones you lose and win.

I think withdrawing the money was probably a blessing in disguise. Don't deposit more. Start anew @ $5NL with a fresh perspective and work your way up both fundamentally AND psychologically.

Good luck.