What does alcohol + ADHD do?
It exacerbates the ADHD, that's all. One way I like to describe ADHD is that it's like being tired all the time without being sleepy. Hard to focus, always kind of drifting off. I like this description because the standard medication for it is stimulants, adderoll, ritalin, hell caffiene can work wonders at times. Alcohol, on the other hand, is a depressant.
The day after I drink, the effect can depend on how much I had to drink the day before. It can range from simply missing my exits constantly when I drive to not even noticing other cars that don't have their brake lights on. It can be like you never even bothered to wake up in the morning even though you're sober, fully conscious, and energetic.