All articles

Why do I feel groggy in the morning?

Last updated: October 15, 2026

Morning grogginess is sleep inertia — a normal physiological transition out of sleep. Its severity depends on which sleep stage your alarm interrupted, your total sleep time, and your circadian timing.

The stage of waking

If your alarm fires during N3 deep sleep, you will usually feel worse than if it fires during light N1 or N2 sleep, with REM in between. Tassi and Muzet (2000) call the sleep stage at awakening one of the most critical factors, although some recent studies find a weaker link (Hilditch & McHill, 2019).

Sleep debt

Sleep loss usually makes inertia worse (Tassi & Muzet, 2000). And short sleep is common: in a 2014 CDC survey of more than 444,000 U.S. adults, about 1 in 3 reported sleeping less than 7 hours (Liu et al., 2016).

Circadian alignment

Waking against your natural chronotype (e.g., a night owl forced to rise at 6 AM) tends to make it worse. In a 2026 nationwide study in South Korea, evening types reported longer morning sleep inertia than morning types: 17.7 versus 14.3 minutes on average (Kim et al., 2026).

Sources

1. Hilditch & McHill, Nature and Science of Sleep, 2019. Sleep inertia: current insights
2. Liu et al., CDC Morbidity and Mortality Weekly Report, 2016. Prevalence of Healthy Sleep Duration among Adults — United States, 2014
3. Tassi & Muzet, Sleep Medicine Reviews, 2000. Sleep inertia
4. Kim et al., PLOS One, 2026. Morning sleep inertia and its associated factors: Findings from a nationwide study