I think I finally figured this out.

Anyhow, beginning of month: Great run at the $100 tables (around 100 BB/100), so I moved up and had a great initial run at the $200 (90 BB/100 to begin with).

Then I kept running into these tight-ish tables and started trying to buy a lot of pots. Well, it worked sometimes, but really just kept losing me money because I didn't know when to quit bluffing (or pursuing marginal hands). I also had gotten so used to doubling up every session that I couldn't accept kind of bleeding away sometimes.

Result of that: Completely annihilated my initial winnings at the $200 but quit LAGging before it got too bad.

My conclusion: Ok, at tight tables, it's ok to try to buy (within reason) sometimes. But you also have to realize that they're still going to give you action with strong hands. So, if your top set or monster draw gets a fold this time, that's ok, it will eventually get a call or raise when they have a hand.

It's just that you can't expect every session to be a winning session, and if you do, you're very likely to make a lot of sessions into losers.