Doctors and scientists aren't really sure why they happen, but they have a few theories. One theory is that your brain misunderstands the sensation of your muscles relaxing as you drift off to sleep. It's normal for the muscles to relax, but the brain gets confused, and, for a minute, thinks you're falling. In response, the brain causes your muscles to tense up so you catch yourself before you fall down.
The former Beatle Paul McCartney has married American heiress Nancy Shevell at Marylebone register office in London. The couple waved to crowds packed behind security barries after they made the short drive from Sir Paul's north London home to the venue.
The pair, also brought their wives along - Ringo is married to former Bong Girl Barbara Bach, who appeared in The Spy Who Love me in 1975, while Joe is married to her sister Marjorie. Rocking out: James McCartney performed at the Viper Room on the Sunset Strip in west Hollywood.