Short Sleep

Several factors influence how much sleep a person requires. The Mayo Clinic has a chart organized by age that includes recommendations ranging from seven hours for adults to up to 16 hours for infants. However, seven or more hours of sleep is at the very bottom of the scale, and doctors generally agree that a lack of sleep can lead to a slew of serious health issues.

Having said that, there are some people who are genetically short-sleepers. The culprit is a DEC2 gene mutation. Those with the mutation can sleep for as little as four or five hours before waking up as refreshed as the rest of you, who require a full seven or eight hours.

The production of a hormone called orexin was altered in mice that had the same gene manipulated. Orexin regulates sleep and wakefulness. When it's time to wake up, your body produces it, and a narcoleptic produces too little. However, those with the altered gene wake up earlier than the rest of you, with no negative consequences. It is considered one of the genetic conditions with remarkably weird symptoms.