Impagination

A psychological state in which one can think of nothing but hob goblins, imps, elves, and related species in inventive scenarios.

Person A: 'Hey do you know the answer for question 3?'
Person B: 'No, I am thinking about imps.'
Person A: 'Ah, I see you have a severe case of impagination.'
Person B: 'Imps : )'