Causes
According to the American Academy of Sleep Medicine there is a wide range of potential causes, including anxiety, caffeine, stress, and strenuous activities in the evening. This strange falling sensation and muscle twitch is known as a hypnagogic myoclonic twitch or hypnic jerk. Close to 70 percent of all people experience this phenomenon just after nodding off, according to a study at the Mayo Clinic.
Most experts agree that this is a natural part of the sleeping process, much like slower breathing and a reduced heartbeat. The occurrence is well known and has been well documented. However, experts are still not completely sure why the body does this. The consensus among researchers is that, as the muscles begin to slack and go into a restful state as sleep is entered, the brain senses these relaxation signals and misinterprets them as indications of falling. The brain then sends signals to arm and leg muscles in an attempt to regain balance. This misinterpretation that takes place in the brain may also be responsible for the "falling" dreams that accompany the falling sensation. These "dreams" are more like a daydream or hallucination in response to the body’s sensations. Various drugs and medications, notably psychoactive drugs, can create jerks when commencing sleep as the body prepares for and initiates muscle paralysis. Opiates such as morphine, heroin and methadone have been reported to cause these jerks with regular frequency along with sudden jerking and waking during the night’s sleep.
While this phenomenon happens to most, studies have recently begun to link some occurrences of hypnic jerks to sleep anxiety, fatigue, and discomfort. People who are having trouble sleeping or cannot get comfortable in bed appear to experience the sensation more often throughout the night. It is especially more common with people who are trying to fight falling asleep or have deprived themselves of sleep for more than 24 hours. Researchers believe that the lack of sleep from sleep anxiety or sleep deprivation confuses the muscles and the brain. The muscles continually attempt to relax and shut down for rest, while the brain remains awake creating continued "misinterpretations" of falling or loss of balance.
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