The strangest thing which ever happened to me was no illusion, but for sure pretty creepy.
I was walking around with this group at my university, and we ran into some friend of one of the girls in the group. I think he was in her lab, or something; at the time I thought so, anyway. He was pretty tall, a little bit taller than me, which annoyed me because I wasn't sure whether or not I might be just as tall, but it was too close to call. I don't know if it was because of that, but I started talking to him because I thought it was very important. Not mysterious, it was probably because I wanted to be smarter since I wasn't taller.
So, I started talking about something random, and then the group I was in wanted to direct us along some line of reasoning, but I derailed it and started talking philosophical nonsense to see what he would do. And he responded, and pretty soon started talking about virtual reality, which I thought was a philosophical idea.
After a bit, he explained it was real, after we had thrown around absurd stuff about virtual reality possibilities. So, I wanted to see it done.
We went back to his lab, and he let me use what I think is called an Oculus Rim. I was absolutely stunned by it, needless to say.
Then I went home after meeting his brother, working on his Ph.D. in Augmented Reality. And then they explained a lot of stuff to me, and then the brother tried to take a picture of us in 3D that could be modeled to create a hyper-realistic 3D sculpture.
So in conclusion, the really weird thing was after I got home. I was sitting in my armchair, and suddenly I realized that I could see to my left.
The reason this was weird was that I have no vision in the left field. After the experiences of that evening, I could see to my left. Not like on the right, because when I compared in front of the mirror, I only had about half as much as on the right. It was absolutely mind blowing.
The next day, things were still functioning. However, over the next week it slowly receded back to where it was before.