It was so real that I still remember it now, 55 or so years later. But I'm certain there was not a tarantula on my pillow.
That exact same thing happened to me when I was a child. I woke up and saw a tarantula on my pillow. It looked as real as anything I have ever seen. I screamed, and my mother came into my room, and the tarantula was gone. I know now that it was a sleep-related hallucination, but at the time, it seemed totally real. It was so real that it disturbed me when my mother did not take it seriously.