Power save mode on Macbook pro

When I shut my macbook pro for around 5 hours at a timeor more, it goes into power save mode (as if my laptop had been fully drained of power and im starting it up again) even when its plugged in and fully charged. Every time I open it back up its frozen for about 15 seconds. I restart my laptop completely about once a week. Whats that all about? also is it bad for my computer/something I should get looked at @ the apple store?