He did not do any damage. He may have strained your neck or upset your vestibular system or just caused a bit of a relapse due to previous issues.

If you look for symptoms, you will find them due to the power of suggestion. If you just ignore the situation, you will be much better.

No matter what, you cannot change what happened. You can only change how you respond.

Whether or not you think your friend should have remembered, he had no responsibility to remember about your condition. But, he should never be grabbing anybody and shaking their head. The neck is just too vulnerable to subtle injury. Being at a concert put you at risk of being jostled. If you do not think you can tolerate being jostled, you should avoid those environments.