During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily.  Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia, often preceded by a sensation of starting to fall. These sudden movements are similar to the “jump” we make when startled.

• Sudden, single, non-periodic, brief local/general muscle contractions, often with awakening
• May be accompanied by visual/auditory/somesthetic experiences
• Occur in 60-70% normal population
• Benign, though may cause insomnia

 Watch video:  All about The Stages of Sleep