Tired, you make the arrangement to go to sleep. You have just dozed off in the comfort of your cozy bed, when suddenly you wake up with a jerk, with a feeling that you almost fell from a rooftop. Now you lay there wide awake thinking about the plausible reasons of the jolt. Was it some bad dream or some ghost pushing you off your bed?
Don’t you panic, you were just experiencing the phenomenon called Hypnic Jerk.
It is commonly called the Sleep Start, hypnagogic jerk, sleep twitch or night start. It is nothing but an involuntary twitch which occurs just as a person is beginning to fall asleep. It may affect only a part of the body, like an arm or leg, but in some cases it causes the entire body to jolt suddenly. In some cases, even a vocalisation or sharp cry may occur. It is estimated that 60-70% of people recall experiencing them. Contrary to the popular belief that these occur in deep sleep, they actually occur in stage 1 sleep which is the lightest stage of sleep that occurs immediately after falling asleep. It may occur periodically later in the night.
These jerks resemble the jump or jerk experienced by a person when startled, accompanied by a sensation of falling into the void. Other characteristic features are a rapid breathing, heartbeat, and sweating etc. These movements may or may not wake you up from your sleep. But if they do they are usually followed by a falling sensation or a brief mental image. The image is a kind of explanation that your brain gives for the jerk, for example, you feel that you were falling off a high building or perhaps kicking the football in your dream. Actually, these movements occur first and are followed by the explanatory mental image.
The nerve theory – As we doze off to sleep, our brain makes the necessary arrangements for our body to relax. Actually, the brain undergoes a shift change to allow the powerful unconscious mind to overtake the conscious one.
The prominent parts of the brain involved are the located in the medial section of the brain and posterior to the optic nerve.
Reticular Activating System (RAS) –This is responsible for handling the wakefulness and keeping us alert.
Ventrolateral Preoptic Nucleus (VLPO) – This part influences our sleep cycle and starts to take over when we doze off.
Slowly as we go to sleep the breathing and heart rates slow down and body temperature drops. The muscle tone shift from alert to relaxed.
According to this theory, during the transfer of control to the VLPO, the RAS makes a last effort to retain control of your body, and this results in the misfiring of nervous signals due to the struggle between the RAS and the VLPO. It stimulates your muscles, causing twitches. Simply put, the jerks are the result of a conflict between the VLPO that wants us to sleep and the RAS that wants to keep us awake and alert.
Evolutionary Cause – You can blame it on your primate ancestors. The primates used to live on the tree and the moment they started to fall asleep their brain warned them of falling off the tree. Therefore, the brain may misinterpret the relaxation of the muscles as a signal of falling off and fires a reflex action to prevent you from the same.
Sleep starts occur more often when the following factors are there:
i. Increased use of caffeine.
ii. Sleep deprivation
iii. Stress or anxiety.
iv. Strenuous evening activities
The hypnic jerks are common and nothing to worry about. So, the next time you experience the jerk, just roll over and go back to sleep because it is just your brain at conflict.