Similar to the feeling of being in a 'K-hole', being in the dungeon is the experience that somebody has whey take a large amount of ket (ketamine), and experience feeling as if they're in an outer body state- Or 'trapped in a dungeon.'
'Dungeoning' is when a large number of people are snorting ketamine in an small area, and stay in that area while the drug taking is occouring.
Often used for torture exercises, a person is placed below a grate in a dark, small, damp space where someone squats on the grate above and fires explosive diarrhea onto the prisoner below.
You better finish your dinner or it'll be straight back to the diarrhea dungeon for you, young man!