it is a command. there is an implied subject before it.
We're not talking about punctuation...
I don't know if it has any real definition, because it is improper grammar.
The statement itself seems more like an interjection. But do interjections even have a category?
I don't think it is a verb, however, because of the way it is used. What are you implying is doing the loving? Or does it mean forget yourself? forget in some contexts can be a noun. It is one of the most versatile words.