You have a drink, you fall asleep quickly, and then — bam — you are wide awake at 3:17 AM staring at the ceiling. This is not random. It is biology.
Alcohol suppresses REM sleep during the first half of the night. When your body metabolizes the alcohol in the second half, there is a rebound effect: your brain surges into lighter sleep stages, causing you to wake up. Your heart rate increases. Your body temperature rises. Your sleep architecture is completely disrupted.
Even one or two drinks can reduce sleep quality by up to 39% according to research. The next-day fatigue is not just from staying up late — it is from your body fighting a toxin instead of repairing itself.