We've all experienced it: You're completely exhausted after pulling an all-nighter, and despite your best efforts to stay awake, your eyelids keep closing and closing until suddenly you nod off for just a second -- only to awake with a jerk.
This phenomenon is what's known as "microsleep," a momentary and involuntary pocket of temporary unconsciousness lasting from a fraction of a second up to roughly 10 seconds, ending in a sudden head jolt.
Why does our brain enter these periods of microsleep? They're typically caused by extreme fatigue. Sleep is a basic biological necessity, and when we force ourselves to go without it for too long, the brain will eventually shut down -- even if just for a few seconds. During microsleep, your brain is essentially taking a forced nap, because its current level of sleep deprivation is preventing certain areas and networks from functioning.
Here's a look at the science of microsleep
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More at source: What's Happening In Your Brain During 'Microsleep'
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no, this wasn't me at 10pm last night. It was 10:20.