Did you ever wake up startled, thinking that you fell? This happens to almost everyone. Usually, this sensation comes to us while we sleep, or at the beginning of sleep.
This phenomenon is known as hypnagogic jerk, which is nothing more than an involuntary muscle spasm, which occurs when a person is drifting into sleep.
These sleep starts are quite frequent, about 70% of people experience them.
A hypothesis about why these hypnagogic jerks occur is that everything is due to a natural response of the body to the adaptation to alertness during sleep, which means that the nerves have a “ignition fault” during the process .