Imagine that you're relaxed and drifting off to sleep when suddenly an arm or leg twitches and you have the sensation of falling out of bed. If this has happened to you, you've experienced what sleep specialists call a hypnic jerk or sleep start. Sleep starts happen in normal, healthy people and don't ordinarily require any medical treatment. However, certain medical conditions can make you jump in your sleep and should be evaluated by your physician.
Most people experience sleep starts, or hypnic jerks, at some point during their lifetime. Sleep starts happen during the transition from wakefulness to stage one sleep, or light sleep. During this transition period, you drift easily in and out of sleep. As you begin relaxing, sudden muscle contractions, also known as positive myoclonus, cause extension of one or more limbs and may also involve the trunk. The movement may be preceded by a sensation of tumbling out of bed or falling off a cliff.
Up to 18 million people in the United States may have a potentially dangerous condition known as sleep apnea. During episodes of sleep apnea, as muscles relax in the throat, the windpipe collapses and interrupts breathing. A person with sleep apnea may stop breathing for up to 60 seconds before the brain directs the sleeper to awaken enough to gasp for a breath. Although this may occur many times throughout the night, most people with sleep apnea are never diagnosed. People with this condition are at higher risk of high blood pressure, heart attack, seizure, stroke and -- because it causes sleep deprivation -- a much higher risk of daytime accidents than the general population.
Restless Leg Syndrome
Restless leg syndrome, or RLS, causes unpleasant crawling, prickling or tingling sensations in the legs and feet during rest, especially at night. The sensations cause an urge to move the legs. Up to 12 million Americans have restless leg syndrome, according to the American Sleep Association. The cause of RLS may be related to abnormalities in the neurotransmitter dopamine. Neurotransmitters help to deliver messages to the nerves.
Up to 90 percent of people with RLS have a symptom called periodic limb movement disorder, according to an article in the August 2012 issue of "Sleep." PLMD involves frequent episodes of jerking of the legs, feet, ankles, toes and hips during sleep, and its presence supports the diagnosis of RLS. However, not everyone with PLMD has RLS. People with PLMD may not be aware that their limbs are jerking during sleep, and the symptoms are often reported by bed partners.
When to Seek Medical Treatment
Sleep starts don't require medical treatment unless the movements are frequent or repetitive enough to disrupt sleep. Sleep apnea is considered a serious health condition that warrants thorough medical evaluation.
If you suspect that you have a sleep movement disorder, discuss the possibility with your doctor. Your sleep movements, especially if they are agitated and occur during the later stages of sleep, might be caused by a serious neurologic condition. Sleep studies consisting of polysomnography and electromyography can be ordered by a sleep specialist or neurologist to assist in making the correct diagnosis.