I had a head injury two weeks ago. I just nearly blacked out lying down?!

I had a head injury two weeks ago. I just nearly blacked out lying down?

I cracked a bus windscreen with my head at 30 miles an hour two weeks ago. I was fine after, no bruise nothing. They saw me at hospital but said i was fine. I was just lying down and suddenly went really dizzy and hot and weird feeling, like the floor was slipping away. My left arm hurts and i checked my pupils in the mirror, but they don't change in the light. Could this just be a panic attack or could my head injury have done something to me?

If you had been well 2 weeks, it seems this is not due to the head injury , don worry, but it would be better to get a check up anyhow.