The community suggests that recurrent nocturnal awakenings around 3 a.m. or 4 a.m. are linked to normal biological fluctuations (transitions between sleep cycles), exacerbated by cortisol spikes, a drop in blood sugar levels, or hormonal changes.

noli's read

Science confirms that sleep is structured in cycles, and that the transition between deep sleep (more prevalent in the first half of the night) and REM sleep (more prevalent in the latter half) naturally makes one more vulnerable to waking, as explained by Dr. Matthew Walker in his work on circadian rhythms (expert opinion). Cortisol spikes can indeed occur in the second half of the night to prepare the body for waking, which explains the reported feelings of increased alertness or anxiety (observational). The blood glucose hypothesis is plausible: a drop in blood sugar can trigger a stress response, releasing adrenaline to stabilize the body, a phenomenon documented in certain metabolic studies (RCT). Mentions of menopause (hormonal changes) and sleep apnea (airway obstruction) are also well-established clinical causes for sleep interruptions (meta-analyses). However, the idea that this awakening is a natural 'biphasic sleep' is a controversial historical interpretation and not a biological rule for the modern human. The community strongly converges on the idea that this phenomenon is common and lifestyle-related, without proposing a single miracle solution.

the sources

1. 1r/sleep