The Jerk that Keeps you Awake

“I shouldn’t be awake this early” you think to yourself.  It was a long night at what was billed as “party of the year”, the third such named event in as many weeks.  Of course the entourage had to stop at the obligatory taqueria afterwards.  Now you’re running on only a couple hours of sleep and didn’t have time to stop for coffee because you would’ve been late for class.  As you sit in the cold dimly lit classroom, you start to feel the effects of the night and the two energy drinks consumed to keep the party going.  The eyelids start to get heavy, and blinks become abnormally long.  “Wake up” you tell yourself, but the desk suddenly becomes very comfortable, your shoulders sag and your head slumps.  The voice of the professor starts to trail off as your body relaxes and consciousness slowly drifts away.  Just as you’re about to cross over into a nirvana of slumber, something shakes you awake with such force that it startles you back into sleep-deprived reality.  You look around but everyone is taking notes just as they were before.  What jerk woke you up?  How dare they!

The jerk that keeps you awake is actually an involuntary twitch known as hypnic jerk.  Brandon Peters, M.D. reports, “A hypnic jerk is an involuntary muscle contraction, sometimes called a myoclonic twitch that occurs during the lightest stage of sleep.  This stage 1 sleep occurs as you begin to fall asleep.  There may be a sensation of falling followed by a physical jerk back to wakefulness.”

Neuroengineering researcher Joelle Barral documents two theories concerning hypnic jerk.  One theory involves the reticular activation system which controls how alert we are.  The jerking and shaking occurs because there is a “misfire” in the nerves of the legs and arms as the RAS makes the transition from being awake to falling asleep.

Another more specific theory says that as you fall asleep there is a transition point where your muscles completely let go and relax.  The brain then interprets the sudden relaxation as a sign that you are falling down, and it makes your arms and legs flail about to keep you from falling, which obviously your not.  The hypnic jerk acts as a protective reflex.

The neurological reasons for this reaction are not fully understood by the medical community, but don’t rush to the emergency room if you have experienced hypnic jerk.  It is quite common, especially in college libraries, and of no medical significance.  One thing is clear, hypnic jerk is exacerbated by irregular sleep patterns.  So if thrashing around in class like a fish out of water embarrasses you, catch some Z’s instead of that free drink.