Sleep is extremely good for the body, and brain, as its when your daytime memories are "written to disk" as it were. "Long term potentiation" or LTP it's called. Sleep is also when your body repairs itself.

I read recently that people sleep much better when their heads are cold. Maybe its the mountain air thats so good for the quality of your rest?

When the air is clean outside I always sleep much better with some ventilation, either a window cracked open or our heat recovery ventilator on.