Hitting a concrete wall at the same speed as hitting a table would cause a higher G force because there would be less deflection ( absorption like a pillow would provide or how a table would move)

Why do you think your speed was 2 m/s ?

Your long question does not make sense to me. You are making assumptions about coup-contracoup (bouncing back) that are not necessarily related to G force.

A lot of coup-contracoup effect is because the head/skull bounces back causing the brain to hit the opposite side of the skull.

You are confusing/combining too many different concepts.