This is called a hypnic jerk . After this rush of activity subsides, the body begins to drift into a light slumber. Stage 1 Sleep is a transition period from wakefulness to sleep. It is characterized by low voltage EEG and slow rolling eye movements. This stage is often considered the official onset of consolidated sleep.
Eye movements stop and brain waves become larger.
Stage 2 Sleep is graphically defined with two distinct brain wave forms called sleep spindles and K-complexes . A K-complex is high voltage EEG activity that consists of a sharp downward component followed by a slower upward component and lasts more than .5 second. Stage 2 Sleep is characterized by a lack of eye movements, sleep spindles and K-complexes. Note the K-complexes and sleep spindles. As sleep advances progressively deeper, an individual becomes difficult to arouse.