A small Australian study found that people who drank alcohol before bed tended to have certain patterns in their brain consistent with disrupted sleep. So even if they felt like they were experiencing restorative sleep, their brain activity negated any positive effect.
That disrupted, alcohol-fueled sleep might even affect how alert you are when you wake up: A 1991 study of 20 adults found that those who consumed alcohol before bed — even just a little bit — were less alert and had a harder time multi-tasking the next day than the group that didn't drink.