I too recovered from my initial concussion and felt 'normal' for a week or two, then got very drunk, and all the symptoms came back.

Concussion involves a lot of chemical changes in the brain, and even after you feel completely recovered the brain has been shown to be more vulnerable to various factors such as stress and lack of oxygen (eg at altitude). My experience is that alcohol is one of the factors which the brain is less able to cope with following a 'mild' traumatic brain injury/concussion.

As much as I used to enjoy alcohol and as much as it was an important part of my social life, I can't risk going back to my post-concussion symptoms, which totally disrupted my life for so long. I am also concerned that the damage I have done to my brain through concussions will increase the likelihood of cognitive decline (eg dementia) as I get older. Both concussion and alcohol use reduce the 'cognitive reserve' that protects you from dementia.

As such I have decided that I will never get drunk again. I am finding other ways to enjoy myself, and it's not as bad as it sounds