Cat Behvaior Help!

[xXJessieMayXx]

My cat is 8-9 years old and he has never been afraid of anything. But for the past 3 days when he would wake my grandpa up to let him outside at 3am, he would walk out of the bedroom and stop, look around as if he was frightened then run like a bat out of (the underground). Just a few minutes ago he ran into my room like a bat out of heck jumped on my bed, meowed a few times (like a distressed, pity sound). Then he jumped off my bed and ran like a bat out of heck. Is this normal cat behavior or is there something wrong? We tried following to see where he runs off to when he is frightened, which is usually to the back door. I've considered he sees ghosts but I highly doubt it (i have 3 dead great grandparents and 2 dead cats, the most recent death was our cat named Scar who was 5 years old and had stomach cancer. my cat now wasnt nice to him when Scar was sick. Scar died in 2008). And I've considered he is just full of piss and vinegar (he will just run around and be a little aggressive), Please help me figure this out.