Around 72 hours without sleep can push the body into an “emergency mode.” Within 24 hours, reaction time slows and attention/decision-making degrade, raising accident risk. By 36–48 hours, mood swings, irritability, concentration loss, and microsleeps (brief unintentional dozing) become more likely. Approaching 48–72 hours, perceptual distortions and sometimes hallucination-like experiences and intense anxiety can occur, especially with night shifts, high stress, or comorbid illness. Immune function, pain sensitivity, appetite hormones, and blood pressure regulation may also be affected. Bottom line: three days without sleep is not “just fatigue”—it is a safety-critical state. Avoid driving and high-risk tasks. Seek urgent evaluation if severe agitation, confusion, chest pain, shortness of breath, or psychotic symptoms accompany sleep loss. Evidence base: systematic reviews describe progressive hallucinations/psychotic-like symptoms with prolonged wakefulness; broader reviews link insufficient sleep with cardiometabolic and neurocognitive risk.