1.   Among ordinary people, sleep paralysis occurs most often after jet lag or periods of sleeplessness that interrupt normal REM patterns.

2.   Another suggested explanation is sleep paralysis.

3.   Europeans seem to have interpreted ancient sleep paralysis as assaults or abductions by witches taking them off for a forcible ride on a broomstick.

4.   Experts have trouble even saying definitively whether a person is asleep or awake during sleep paralysis.

5.   Moreover, a growing number of scholars believe that sleep paralysis may help explain many ancient reports of attacks by witches and modern claims of abduction by space aliens.

6.   Other defenders of abduction theories say aliens may be clever enough to use sleep paralysis in their kidnappings.

7.   Sleep paralysis was once thought to be very rare.

8.   So what is sleep paralysis?

9.   Sleep paralysis sometimes runs in families and appears to have a genetic component.

10.   Still, sleep paralysis cannot be a full explanation because some reports of alien abduction do not involve sleep.