Why am I tired even after a full night of sleep?
Total sleep duration is only one factor. Sleep quality (fragmentation), timing relative to your chronotype, and the sleep stage you wake from all influence how rested you feel.
Quality vs. quantity
Broken sleep (frequent wake-ups, a snoring partner, alcohol) is less restorative than the same amount of unbroken sleep (Stepanski, 2002). Questionnaires such as the Pittsburgh Sleep Quality Index measure quality as well as duration.
Wake stage
Waking from N3 deep sleep produces more inertia than waking from lighter stages (Tassi & Muzet, 2000), even after a good night, although the size of the effect varies between studies.
Hidden disorders
If tiredness persists despite 7–9 hours and good habits, ask a doctor about sleep apnea, periodic limb movement disorder or thyroid problems. A sleep study can detect the first two; thyroid problems need a blood test.
Sources
- Tassi & Muzet, Sleep Medicine Reviews, 2000. Sleep inertia
- Hilditch & McHill, Nature and Science of Sleep, 2019. Sleep inertia: current insights
- Stepanski, Sleep, 2002. The effect of sleep fragmentation on daytime function
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