Hypnic jerk
In a meeting... Working on a report late at night... With your Oceanography class at the IMAX theatre in Darling Harbour... It could happen at any time. What is it? The dreaded hypnic jerk.
Dreaded? Oh yes - you really hope nobody just noticed that!!!
A myoclonus, also called a myoclonic jerk, is a quick, involuntary twitching of a muscle or group of muscles. Hiccups are a form of myoclonus where the diaphragm is the offending muscle. Brief muscular contractions are called positive myoclonus, whilst relaxations are called negative myoclonus.
Myoclonic movements are commonly seen during induction of general anesthesia with intravenous medications. Hypoxia (a lack of oxygen) may result in posthypoxic myoclonus. However, the specific mechanisms underlying myoclonus are not yet fully understood.
One of the most common types of myoclonus is the hypnic jerk. These are often experienced just before falling asleep. This is when people experience hypnagogia, the state of intermediate consciousness that is the transition between wakefulness and sleep. Physically, hypnic jerks resemble the jump experienced by a person when startled, and are often accompanied by a falling sensation. People with an irregular sleep schedule report a higher occurrence.
One theory is that as the body enters this very relaxed state, with breathing slowing right down and brain activity decreasing, the brain can be fooled into thinking the body is shutting down. So it does what any good brain should in these circumstances, and sends a shock throughout the body, as a kind of jump-start. The result is the hypnic jerk.
So the next time you experience a hypnic jerk in public, don’t try to hide the fact. Look around with pride, because your brain is working hard to keep you alive :)