As a nurse, i worked many evening, night and double shifts in hospitals. My friends and I were obsessed with our sleep, or lack of it: How long did you sleep? Was it good? The body’s circadian rhythm — an internal biological clock that regulates a variety of functions — is easily interrupted by this kind of shift work, as well as by travel across time zones.
When American travelers make plans to visit Portugal, Lisbon is usually their first stop.