When you are feeling more tired and sleepy, the body takes you to sleep fast. Suddenly you feel a jerk, like falling from somewhere. It is a very normal condition where each and every one of us would have felt this at least once. So what is going on here?
All our muscles get relaxed while we are sleeping. There won't be any movement. This makes the brain to get confused.
For a second, the brain misinterprets the relaxing of muscles as a sign of actual falling and signals the muscles to tense up, in order to protect you.
The body jerks creating a feeling to "catch yourself" before falling.
Most of the people falls right back asleep afterwards.
It goes after the term "Hypnic jerks".