Was watching the PJ for a few hours tonight, and just a few minutes ago, things suddenly became very dark. The darkness is a little more pronounced toward the top of the lcd (bottom of the projection), but the whole thing has dimmed immensely.

I turned everything off immediately and opened up the case. No word yet if it's fixed anything, I wanted to let it cool for a while. Am I right to guess that I overheated the lcd?

LCD goes balck when it overheats, supposed to fix itself when it cools. Not recommended but supposedly doesn't hurt LCD YMMV

Yeah, what your describing sounds more like something slipped out of place in your light path somewhere.
If you cooked your LCD, you probably would have seen a black spot in the center first.

But like Pcam says YMMV

usually a dark spot in centre, that grows,, how ever could be still a general over heat that will cause it to go dark overall, stick a thermo in there and measure it,

you must not have enough airflow,, upon reviewing what you wrote,, where ever the temp reaches saturation,, it will go dark, also another nastier effect is that the ffc's let go because the adhesive also reaches it soft point,, so increase ya airflow

Everything has cooled off and is working fine again as far as I can tell. My airflow is definitely lacking, but it's never been a problem up until now.. Maybe the ambient temp in the room was higher than normal?

In any case, I'll definitely work out a way to get better flow over the lcd. I can't afford to fry it!