Constant sleepiness (excessive daytime sleepiness) can be due to simply not sleeping enough, but not always. The most common driver is insufficient or fragmented sleep from irregular schedules, screen exposure, and stimulant/sedative cycles. A major medical cause is obstructive sleep apnea (snoring, breathing pauses), followed by movement-related sleep disruption (periodic limb movements, restless legs). Other contributors include depression, hypothyroidism, chronic pain, sedating medications, and metabolic issues. If someone reports adequate sleep hours but struggles to stay awake in passive situations or while driving, or has morning headaches/dry mouth/snoring, sleep apnea should be ruled out—often via a sleep study. Approach: quantify sleep duration and regularity, then evaluate for apnea/RLS and medical/psychiatric contributors. Evidence base: reviews of excessive daytime sleepiness causes and risk factors; NHLBI/AASM guidance on sleep apnea diagnosis.