Nearly all animals in the animal kingdom have multiple sleep episodes per day. Sleeping just once per 24h period is an anomaly, and may partially be an artifact of artificial lighting. Most adult humans are naturally wired for sleeping twice every 24 hour period -a 6-7h nocturnal rest with a 20-60m siesta in the afternoon. Sleep patterns defined by more than one sleeping episode every 24h period are called polyphasic sleep.
Polyphasic sleep has created a buzz on the Internet lately. Self-experimenters usually try one of two schedules:
- Nap for 20 minutes every 4 hours (total of 2h per day), or
- Have a 3h "core sleep" at night with three 20m naps in the day (total 4h per day).
Polyphasic sleep seems to be the only way to function on less than 5 hours of sleep (for genetically non-short sleepers). Unfortunately, our of all the people who try to adapt to such a schedule, the majority fail, suggesting that some people just aren't wired for this.
Polyphasic sleep is an interesting sleep schedule that some people use with success, but the topic is too detailed to cover fully here.
