Is it possible for me to trick myself into seeing a ghost in order to believe someone?

So my GF sees ghosts, and is deeply religious. Also, she was young when she saw a close relative of hers die. I've heard people can be open to suggestions especially when religious to see ghosts. One night when she was being haunted by one of the bad ghosts, I prayed for her(something I rarely do since I haven't been religious for the longest time until after this night) and about 5 minutes after while cuddling and trying to help relax her, I saw that the wall was lit up. I turned around to see what was causing the light and there was an orb of light, it glowed and filled the room, then retracted the light into itself and disappeared. I freaked out and asked her if it was the demon, found out from her the next morning it was apparently St. Micheal trying to let me know he heard my prayers. As a heavy skeptic I'm having a hard time even believing myself, even though I have no physical explanation (and trust me I tried to find a reason why I may have mistaken that for something else but nothing fits the bill) for what I saw and I'm believing it could have been a religious experience. Before I rule everything out, is it possible that I somehow tricked myself into believing I saw that? It's a rather odd thing to hallucinate since in my mind I expected a ghost to be a human figure. Is there any psychological explanation for me seeing that? I was sober, I've been MUCH more sleep deprived without hallucinating, and it was fairly brief about 3-4 seconds, so not a split second where I mistook something.