What it isA state of persistently elevated threat-detection: the brain’s alarm system locked in the ‘on’ position, continuously scanning the environment for danger even when none exists.

Why it mattersIn veterans with PTSD, hypervigilance doesn’t shut off at night. This sustained arousal directly interferes with the brain’s ability to enter deep sleep stages and is a key mechanism linking PTSD to sleep apnea.

Think of it like thisImagine trying to sleep while someone keeps poking you to check if you’re still awake. That’s what a hypervigilant nervous system does to itself all night, preventing the deep muscle relaxation sleep requires.

Hypervigilance is a symptom of post-traumatic stress disorder defined in DSM-5 as markedly elevated, sustained vigilance for environmental threat, associated with HPA-axis dysregulation, noradrenergic hyperactivity, and amygdala sensitization. It belongs to the arousal and reactivity symptom cluster of PTSD.

MechanismDriven by amygdala hyperactivation, suppressed hippocampal regulation, and excess norepinephrine release from the locus coeruleus. The locus coeruleus-norepinephrine system maintains chronically low arousal thresholds, preventing transition into slow-wave and REM sleep. Chronically elevated cortisol and sustained sympathetic nervous system activation reinforce the cycle. In the context of sleep apnea, hypervigilance may prevent the deep pharyngeal muscle relaxation that normally keeps the airway open, or may lower the arousal threshold such that the brain responds to normal respiratory fluctuations as threats.