The director of Columbia University's Medical Center found that people who sleep on buses, trains and planes likely benefit from it.
They probably only reach the lightest stages of relaxation -- stage one or two -- but that can be enough to re-invigorate morning commuters who got a bad night's sleep.
In the afternoon, those naps can be frustrating because a person might want to slide into stage three or four of sleep, which is the "deep sleep" phase.
