Alcohol's cost shows up less in falling asleep and more in the sleep stages that come after.
Alcohol's relationship with sleep is a case study in how something can feel helpful in the moment and still work against you overnight.
A night's sleep cycles through stages — light sleep, deep slow-wave sleep, and REM sleep — each serving different restorative functions. Deep sleep is heavily involved in physical recovery; REM sleep plays a large role in cognitive and emotional processing.
Alcohol can shorten the time it takes to fall asleep, which is part of its reputation as relaxing before bed. But as it's metabolised over the night, it tends to suppress REM sleep in the first half of the night and fragment sleep in the second half, leading to more night waking — even when total hours in bed look normal.
This is why a night of drinking often shows up more clearly in a lower Sleep score than in the Alcohol contribution itself. The two pillars are tracked separately in THE FAD, but physiologically, they're deeply linked on nights you drink.
Practical takeaway: if you notice restless nights after drinking even when you "slept enough" hours, this is very likely why — the issue is architecture, not just duration.