Computers do shutdown at certain temperatures to prevent melting down.
Laptop might be dusty. Could be time to clean it out.
What framerate is the game running at? You might have vsync disabled or something, letting it run at 100+ FPS. If turning vsync on doesn't help, you might try a framerate limiter. Turning the graphics settings down would also help with that (although there's not much to turn down in this game). I've also got a mod somewhere that reduces the amount of detail in the overworld tiles so there's less to render (there's a lot of unnecessary detail).
