Something that is funny but you don't really know why. Usually results in some form of uncontrolled laughter over an object/person/situation normally considered uninteresting.

Whysterics are most common after a run-in with death, or during the consumption of substances legal or otherwise.
(Person 1 sees a cow eating grass in a field.)

Person 1: "Ahhahahahahahaaha! That cow! Oh my god! Sooo funny! Urgh, I'm dying!!"

(Person 1 continues to laugh uncontrollably.)

Person 2: "Dude..."

(Person 2 looks at Person 1, confused.)

Person 2: "Man you're having a proper Whysterical moment, what've you had?"
by ScarletVincent November 21, 2010
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