The flash of light does not mean a concussion. Many get that during a hard sneeze.

The chair incident was a sub-concussive impact. If you got hundreds of those during a football season, you would have a problem. The brain can tolerate an occasional sub-concussive impact with no problem.

I don't think either was a concussion. Your anxiety about concussions is taking you for a ride. And, drop the TBI and even mTBI concept. That just feeds your anxiety. Stop checking for symptoms. The brain is very susceptible to the power of suggestion. If you ask yourself "Is my vision OK?" You will notice something that appears to be wrong.

If your vision feels off, get an assessment by a professional. Don't try to self-diagnose. Take care of your neck and things will get better.