Sleep is an important aspect of every human being's life: we rebuild lost muscles, repair damaged body parts, and rework all the work done during those days. As we age we need less sleep because we are not evolving as much as we did in earlier ages. When we are newborns we need 16-20 hours of sleep per day, then at the age of 3-5 years this decreases to around 11-13 hours of sleep per day. During adolescence it is a healthy choice to sleep 9 hours a night. Adults recommend around 8 hours of sleep. Although some people say that even after a long session of drowsiness they still feel sleepy and groggy. This can be traced back to the fact that they may have been woken up in the middle of a sleep cycle. The body is in a deep sleep and it is not necessary, physically or naturally, to wake up during this stage of sleep. Power naps might be a plan designed to refresh your body, but it all depends on how long you rest. 20-minute power naps will help your brain cool down a bit, but the more time you spend, the more dangerous it becomes to get into the zone where when you wake up you'll feel groggy and worse. An hour and a half is a...