The difference is when you imagine things normally you are aware that you are imagining them and you have full control over them. I can picture an elephant in t

The difference is when you imagine things normally you are aware that you are imagining them and you have full control over them. I can picture an elephant in the room with me, I can change its size or color, I can give it a top hat, and critically I can make it go away at will. If you're hallucinating, it's just there, however it happens to be, and while you might be able to reason that it's more likely a hallucination than reality, that doesn't make it feel any less real, nor give you control over it.