I suffered a minor concussion 9 days ago. My only lasting symptom was a minor headache which ceased about three days ago. Can I drink tomorrow night?

Wouldn't recommend. After a brain injury, it would be better to avoid alcohol and any other nervous system depressant for quite a while. Remember, it the only one your have or will ever get. Take care of it now. It has to last a life time! discuss this with your pcp, neurologist or ns who treated you.