Just because a drink before bed can make it easier for you to fall asleep doesn’t mean that it actually helps you sleep well. Drinking alcohol can reduce the benefits of your sleep.
Alcohol disrupts the rapid eye movement (REM) sleep cycle, which is when you dream. It’s considered the most restorative sleep state. Typically there are six to seven cycles of REM sleep. Usually, your body falls into a REM cycle after about the first hour and a half of sleep, but alcohol can actually reduce the effectiveness of that sleep stage or even cause you to skip the first cycle.
Alcohol consumption leads to missing several REM cycles, which leaves your mind sleep-deprived. The REM cycle restores your brain while the deep sleep cycles restore your body. Since alcohol can put you directly into a deep sleep, it gives off the sensation of having had a restful sleep, but you can wake up mentally exhausted. This is why staying asleep for more than a few hours after drinking can be difficult. This can have a cumulative effect to the extent of having the same issues even after abstaining from alcohol.
Alcohol makes sleep apnea worse.
Alcohol use exacerbates sleep apnea risk because it inhibits your body’s ability to breathe while sleeping. Alcohol relaxes the muscles in your throat making it more likely for the upper airway to partially collapse, causing snoring or become fully obstructed causing an apnea event. Most doctors will agree that one to two drinks will only cause a minimal effect (depending on other health factors, including your BMI), but any more than that can adversely affect your much-needed rest.