If you've ever slept in a hotel, gone camping, or even slept over at a friend's pad, chances are you've woken up the next day feeling groggy and bleary-eyed. Even if you don't remember tossing and turning, you probably felt pretty tired the next day. Well, that's because nature dies hard. When we sleep in a new place, our brains are actually in survival mode, only turning half off, with one hemisphere remaining more "awake" than the other. Scientists from Brown University who discovered this phenomenon suggest that it makes us better able to jump awake when strange sounds approach. Their findings are published today in the journal Current Biology.