失眠 (shī mián) literally means 'loss of sleep' — 失 (shī) means 'to lose' or 'to miss', and 眠 (mián) means 'to sleep'. Together, they form a compound noun meaning 'insomnia': a persistent difficulty falling asleep, staying asleep, or waking up too early, resulting in poor-quality or insufficient rest. It’s a clinical term used in both medical contexts and everyday conversation to describe chronic or occasional sleeplessness.

This word is commonly used when discussing physical or mental health, stress, lifestyle habits, or aging. Unlike casual phrases like 'can’t sleep', 失眠 carries a stronger implication of recurring or problematic sleep disruption that affects daily functioning. It often appears in discussions about anxiety, depression, work pressure, or poor sleep hygiene — for example, doctors may ask patients whether they suffer from 失眠 during health assessments.