Sleep starts (hypnic jerks) are sudden, brief jerks that occur when a person is falling asleep.35 They are often associated with a subjective feeling of falling, a sensory flash, or a sleep-onset dream.36 Between 60 and 70 percent of the public experiences sleep starts.37
Although simple sleep starts are benign, there are more complex motor behaviors that may be associated with, or misinterpreted as, “sleep starts” which might be symptomatic of a more serious condition, such as restless legs syndrome (RLS).38 Thus, the importance of recognizing simple sleep starts is primarily in distinguishing them from other conditions that may require further evaluation or treatment.
The etiology of sleep starts is not understood, but they can be precipitated by an increase in caffeine intake or intense physical activity just before bedtime.
Sleep-onset insomnia and/or sleep deprivation may occur if sleep starts become repetitive or intensified. In such cases, short acting hypnotics may be prescribed to facilitate sleep onset. 39
35 Thorpy MJ, “Classifications of Sleep Disorders,” In Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, page 687.
36 Thorpy MJ, “Classifications of Sleep Disorders,” In Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, page 687.
37 American Academy of Sleep Medicine (AASM). International Classification of Sleep Disorders, 3rd edition: Diagnostic and Coding Manual. Darien, IL: AASM, 2014.
38 National Institute of Neurological Disorders and Stroke, Myoclonus Fact Sheet, Bethesda MD: NIH, 2014. http://www.ninds.nih.gov/disorders/myoclonus/detail_myoclonus.htm
39 Sander HW, Geisse H, Quinto C, Sachdeo R, Chokroverty S, “Sensory sleep starts,” J Neurol Neurosurg Psychiatry 1998;64:690.