As you correctly pointed out (and as I've come to realize myself after having slept on it) my problem is - paraphrased - paranoia. My hand reading skill is actually pretty decent (I'd like to think so, anyway) but when I get re-raised, I re-evaluate and usually decide that the worst possible scenario is what has happened. Essentially, my fear clouds my objective thinking.
Looking at the hand afterwards, with no emotions invested, it's clear that I most likely had the best hand. No one capped the flop. Although it's possible that someone would have hit the flush on the turn, I have to bet. If I get check-raised on the turn by the hand I figured on a draw (which in this case would have been UTG+1), I might have laid my hand down. I put the CO on KK after the flop (which turned out to be correct, by the way - yay me), but I had no idea what to do with MP3. He's the one I was afraid held QQ.
So I checked the turn, fearing a check-raise. That was dumb. But not value betting the river is a disaster! See, here comes another impulse that I need to keep in check (ha-ha?): I didn't check for a good reason. At this point, I was so overcome with the idea that my rockets were beaten that I checked to end the hand as soon as possible, so I could find out. It's dumb.
Fortunately for me, it's not something that's likely to happen again. That's the beauty of experience, isn't it?
Anyway, you're sort of right. It's not primarily reading that's the problem (although it was with MP3), it's first and foremost my lack of confidence in my reading when people act differently than I would have in that situation. Schoonmaker calls this the "egoistic fallacy"; we expect other poker players to behave like we do.
So, to recap: I placed UTG+1 on a draw and CO on KK. I was right in both cases, although UTG+1 was going for some weird sort of runner-runner gutshot. I don't know what he was doing in that pot at all with KTo. MP3, as it turns out, held AQo.
I spent the latter part of last night reviewing the traits of the tight-passive player (in Schoonmaker's "Psychology of Poker") to see if this description fits me. It doesn't - by any counts I'm to the aggressive end of the passive/aggressive scale. But I still need to learn to take a deep breath on the turn and think things through for a few seconds and not check fearing the doomsday scenarios. It's stupid, and it's costing me money.
Thanks, XD, I appreciate it.