The phenomenon of sleeping less after a night of drinking. May or may not involve crashing because of alcohol. A person wakes up earlier and is unable to fall back asleep because of an interrupted REM phase, and results in a gradual tiredness.
A: Yo, I have a serious hangover, dude
B: I don't, but I got alcohol insomnia. Woke up at 6:00 this morning and now I'm dead tired