It is a myoclonic or hypnic jerk.

This is called a Hypnic Jerk and 60 - 70 people in the world get them this is very common so there is no need to worry. Hypnic Jerks can either be in your leg or your whole body.

This body movement during sleep, known as a hypnic jerk, is believed to be a natural occurrence when the body transitions from wakefulness to sleep. It is thought to be due to a sudden change in muscle activity as the body relaxes.

Sometimes, the brain misinterprets the changes in the body as it falls asleep (lowered temperature, relaxing of muscles, slowed breathing) as the beginning of death. Hypnic myoclonia is used as a survival mechanism in an effort to revive the body.

Yes, because a jerk is a jerk, they would be likely to like another jerk!