Originally just the definition for getting a relaxing "high" from smoking sheesha but has been adapted to mean getting high, drunk or super ma'fuck'n done.
Thomas: Mrs. Parr, I just wanna get sheeshed.
Kirk: Yeah man, pass that water bottle. *takes a drink* fuck, that's rough!
Mrs. Parr: Oh, you guys...
When you're so high from tree+dabs you think of another word for being extremely high. Replacing zooted/stoned/retarded etc. The term was originally coined by Action Bronson on Viceland's "Travelling the Stars with Action Bronson, Ancient Aliens 420 Special"