The chemical that tells plants when it`s time to sleep
(PHYSorg.com Biology)

Each of us goes through a daily cycle. We wake up, spend the day eating, working and playing, and then we sleep. Messing with this cycle by not sleeping, doing shift work, travelling to a different time zone or living where there is 24 hours of light or dark can really interfere with our wellbeing and our long-term health.