An interesting report notes that when you sleep in a new place, only half your brain gets a good night’s rest.
The left side of the brain stays alert when sleeping in an unfamiliar place for the first night. Researchers found that playing irregular beeping sounds into the right ear (thereby stimulating the left hemisphere) is much more likely to wake up a person than playing the same sounds into the left ear (and stimulating the right hemisphere).
This has been described as a first-night-only phenomenon because it only happens when a person is sleeping in a new place for the first time. Presumably, this behavior of the brain is an evolutionary adaptation that happened in an ancient time when humans sleeping in a new place were at risk of being attacked by predators and needed to be on alert.