I had an encounter and actual fight with a physical creature who's form I could not comprehend. Whenever I looked at it I could see it, but couldn't grasp it's appearance. It also seemed to radiate fear and was clearly hostile. I used my serious anger issues (my friends call it my "unnatural rage" because they're convinced it's not natural. People claim they can feel it in the air when I'm pissed.) to get past the fear and attack it. After I hit it, it oozed away in a direction I'd never seen before.
My Mom said it was a demon, my friends said it was an extra-dimensional predator, my Dad said there was probably a logical explanation after failing to come up with one.
My life is weird, but that was some Lovecraft s*** right there.
I've never even had nightmares that came close to that level of messed up.