Barking alert!

Hello guys… Well, this event happened some days ago and scared the shit out of me… Well, I was in my room with my dog. My parents were away and I was playing computer games like usual and my dog was sleeping by my legs, when he (my dog) suddenly woke up and went to my bed and started barking. I stared at him and he was all freaked out. He kept barking and jumping on the bed and just barking at the wall… I tried to pet him and set on my bad, but he kept moving and just kept on doing what he did.

I was so scared… What do you think was that all about, do you think there is something wrong? Please tell me! Pretty please.
O.o