I was in the back seat of a car (regular Uber) when the driver pressed the acceleration suddenly. This caused my head (along with part of my upper body) to move back suddenly due to inertia (not whiplash, but just glided backwards and stopped), but didn't hit anything behind.

Throughout this, I had grabbed the hand support above the windows.

This happened twice in the same car ride, in an interval of 15 minutes.

I didn't have much symptoms after that, apart from a little nauseous feeling, which went away after a few hours of rest (might be due to inner ear balance issues).

Is this equivalent to a sub concussive force (akin to header in soccer)?

Also, I'm worried that the brain might have hit the back of the skull due to sudden acceleration. Is the g force enough to cause a collision of brain with skull, or do the CSF and other layers would've prevented this?

Thanks in advance.