Hopeful,

Welcome to NeuroTalk.

Your don't really say what your injury was. "Slipped on my back...."

Did you hit your head or just get whiplash or....?

Bumping your head under the car with no description of any immediate symptoms is just a bump.

It sounds like your concern is about possible damage and such. That is a dangerous thought process to continue. Many ruin their lives by worry about "Did I cause brain damage when I laid down too fast on my pillow?" or when I bumped the door frame as I got out of the car or any of a myriad of head contacts

As you say, The bump startled you. That suggests an anxiety response. Anxiety can cause a person to feel out of it.

An undiagnosed upper neck injury from whiplash or other head/neck trauma can cause almost every symptom that a true concussion can cause.