Why?

[Kay]

Do we say "She's been sat on her A**E" or  "Get up off your A**E"???   I say it but its physically impossible so Im just wondering how this saying came about!

[Quizmonster]

The prepositions, 'off' and 'on' are frequently used in peculiar ways, Fina! Someone who is "off his head" has not been decapitated and someone who is "on drugs" is not standing on a sack of cannabis! Just another of the delightful anomalies of English.