Noun - When you laugh, but then forget what was so funny in the first place.
I laughed so hard at Happy's joke that I forgot why I was laughing; I must have lolzheimer's.
a mental condition similar to dementia that occurs when you are really high. Symptoms include occasional memory lapses, confusion, emotional instability, and forgetting where you are or what you were doing.
Man 1: What are you doing with that cheeseburger in your pocket?
Man 2: Shit, I don't know... Damn! I've got Lolzheimer's again.