'First Night' Insomnia: Why You Don't Sleep Well in a New Place

The study involved 35 people who spent several nights in a sleep lab while the researchers monitored their brain activity using advanced brain-imaging techniques. The results showed that during the first night, the left hemisphere of the brain was more active during deep sleep (or "slow-wave sleep") than the right hemisphere. This difference in brain activity is similar to, though not as drastic as, what is seen in marine mammals that sleep by shutting down just one half of their brain at a time