So why do you wake up so early?
There are a few reasons you can’t sleep in as late as you’d like. For one, your sleep cycle gets messed up. “You have two types of sleep: non-rapid eye movement (NREM) and rapid eye movement (REM),” says Mansour. REM sleep is where you go into a lighter, dreaming state, and these short intervals are mixed in between deeper, NREM sleep, which restores the mind and body and repairs muscles. Your body goes through cycles of the two types during the night, and each time you go into REM sleep, the interval gets longer (the first can be just 10 minutes, the last can be almost an hour).
“When you drink, you actually fall asleep faster and go into deep sleep faster,” he says, so your initial bit of sleep might feel ~amazing~. But disruptions to your sleep cycles (keep reading to understand why those happen) ruin the natural transition between REM and NREM, and as a result, you don’t get as much REM sleep. And, actually, studies show that disrupted sleep actually makes you feel worse in the AM versus just not getting enough sleep.
While your sober sleep may be disrupted by the occasional bathroom run, your drunk shut-eye has even more potential interruptions, thanks to your body’s attempts to process the alcohol while you’re asleep: For one, a chemical process called glutamine rebound can stimulate your body and wake you up, says Mansour.