I had a very realistic visual hallucination once (hypnopompic). I was coming out of a nap while I had a fever. I looked over, and beside the bed was a young woman staring at me intently. She leaned over to bite/eat me, but calmly and without any emotion. As soon as she got within touching distance of me, she started to vanish, from the centre-out, and within a couple seconds was totally gone.

I was really struck by how real she seemed. She looked exactly like a real person.

But I just knew she wasn't real (the same way that you just know things in dreams). Because of that, I didn't find it scary at all. I remember being a little curious what kind of sensations I would "feel" when she actually made contact with me, and was a mixture of disappointed/relieved when she vanished at that point. But strangely(?) not scared.