Hey there Tony, welcome to DreamViews!

It's hard to say exactly what happened, but my best guess is that you were asleep up until the point where you ran back to your bed, then perhaps you actually woke up and called for your grandma.

I had some similar experiences when I was quite young -- one of them involved seeing a hand on a long arm (mechanical maybe?) coming out of the attic and pulling at the covers on my bed. I was screaming for my parents, and they came in. Of course, I was running a high fever at the time, and they ended up taking me to the hospital, so that could have been a fever-induced hallucination.

Anyway, I hope you stick around the site, and learn about lucid dreaming. It can be a lot of fun, and a great way to help overcome any fears you may have, or eliminate nightmares.