I played the game through on normal, everything was beautiful and smooth. Then I started a Toorum mode game, everything was still beautiful. But after setting it aside for a couple of weeks, now I go back and find I'm getting choppy framerates. Haven't updated any drivers (to my knowledge). What is even stranger, is that in one hallway, the framerate is low if I walk in one direction, but if I turn 180 degrees, it's fine. The hallway is dark, no torches in sight. Anyone have any idea what could cause this change? Lowering the graphics settings does not fix the problem and my new laptop shouldn't require that anyway.

The only thing I've installed since the last time I played is Spacechem (also from GOG).

Occasionally the game takes forever to load, and after a couple minutes in game, the framerate is extremely low.

Feeling a bit stupid now. Somehow, the power management setting in windows was changed from 'high performance' to 'energy saving'. Switching it back to high performance resolved the issue. If anyone should come across the same problem, you may just need to learn more about how to use your own computer.