REM Sleep: The Dreaming Stage
About 90 minutes after falling asleep, the body enters REM (rapid eye movement) sleep. Brain activity nearly matches wakefulness, heart rate and breathing become irregular, and vivid dreaming occurs. Throughout the night, the body cycles through these stages 4–5 times, with each cycle varying in length.
Why Hypnic Jerks Happen
Hypnic jerks occur during the transition from wakefulness into stage one sleep. Sleep specialists suggest they are essentially misfires of the nervous system. Rafael Pelayo, a sleep expert at Stanford Sleep Medicine Center, explains that during this transition, parts of the nervous system may “switch off” at different times, leading to a mix of signals that cause sudden muscle contractions.
Interestingly, hypnic jerks are more common when someone is sleep-deprived, stressed, or consuming stimulants like caffeine before bed. In cases of extreme fatigue, the body sometimes skips straight from stage one into REM sleep, bypassing stages two and three altogether. This rapid transition appears to increase the likelihood of hypnic jerks, acting almost like a red flag from the body saying: “You need rest, and nothing else will substitute for it.”
