I suffered a concussion when I was aulted, is it unusual to have physical affects 2 1/2 weeks later?

After the ault, I sought medical attention 41/2 days later only to learn my benefits were terminated because my company failed to pay the premiums. A long story short while waiting for my benefits to be reinstated, I slept thru an entire shift and just could not recall that I failed to call in sick that particular morning! Even though my company of 16 plus years knew I was waiting to see a doctor, they fired me for" No call, No show!" As I prepare for Arbitration my thinking is a Medical Opinion would certianly weigh in my favor? Any professional opinions would certianly be appreciatted!