A universal term used for a variety of reasons and in different situations such as: distress, happiness, confusion, humour, boredom, ecstacy..etc.
However the speaker sees fit to use it is proper. Please note, the two founders of this sacred word are Kat n Ally. The only philosophers of the word, and can only know the true true reason behind it.
Kat: Immeh, immeh. I forgot my lunch!
Ally: Oh, immeh! U can have some of mine.
Kat: Immeh! Thanks!
Ally: No probs, immeh-head.