To define a roflseizure, you really need to have experienced one.
Some say the feeling would not be dissimilar to that of raucously laughing whilst simultaneously having a seizure of some sort.
Roflseizures can be caused by the laughing itself or a number of alternative factors such as; severe trauma (psychological/physical), psychadelic drugs.

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life