Is there a verb opposite of "to exist"?

I can say that something exists or that is does not exist. Should there not be some way to express the opposite of the verb "to exist" as a substitution? Or can something the doesn't exist be allowed to have a positive verb at all? Or do verbs ever only have one opposite? "not sit" could be "stand" or "lie", so that wouldn't, but "not breathe" seems to be "suffocate" and maybe not anything else.

Solution 1:

there are many words:Nonexistent, it was Imagined or be Imaginary, it could be a hallucination or be hallucinatory, fictional or fictitious, illusory, fanciful.

I could go on, but the links have synonyms too.