Black figure shadow strangling me in a dream?

I was dreaming, i was with my friends and a black car starts to drive by, i knew it was bad cause i felt fear i "woke up" before it past me. i woke up in my dream in my room and a black figure shadow came from my left side and started to strangle/choke me. i wanted to scream but i couldn't and i tried to move and hit the shadow but my arms wouldn't move. i felt great fear as this was happening. i finally woke up and was gasping for air. can someone please tell me what this means, or if something is actually there.