Do you feel less well-rested after crashing at a friend's place? You may have more than an uncomfortable futon to blame. new study found that when you're not in your usual bed, you may only be sleeping with half your brain.The tendency to sleep less soundly away from home is so common that it has a name among sleep specialists: the first-night effect. In order to determine the source of this phenomenon, researchers from Brown University monitored the brain activity of 11 people while they slept in an unfamiliar place.The typical brain signals that represent deep sleep were only present on the right side of participants' brains. In other words, their left brains remained half awake throughout the night. Yuka Sasaki, one of the study's authors, told CBS that this may be the brain's mechanism "to keep watch" on your surroundings.This pattern lasted throughout the first night, but fortunately, things evened out afterward. So, if you're planning a trip, your best bet may be to schedule your most demanding activities after the first day, once you've gotten the chance to sleep with your whole brain.