In Detail
Sleeping a sufficient number of hours and waking feeling rested are two different things. Sleep quality — the depth and continuity of sleep, the proportion of restorative deep and REM stages — matters at least as much as duration. The most common reason adults sleep enough but still feel tired is undiagnosed sleep apnea, which fragments sleep architecture without the patient being aware of waking.
Other contributors include hormonal imbalances (low testosterone, perimenopausal night sweats, thyroid disease), alcohol use in the evening (which suppresses deep sleep and disrupts the second half of the night), late caffeine, untreated anxiety, certain medications, and underlying medical conditions including anemia and chronic inflammation.
A proper evaluation considers sleep quality as a clinical question in its own right, not just total hours.