I can personally attest that it is extremely hard to drive with concussion symptoms. Far worse than being totally drunk. You can see, but you lose track of what things are. In my case, I slowed down, veered to the side, then banged into a parked car. I could see the car, but I could not think of what to do to avoid hitting it. Thing is, the previous day I had been knocked flying from my bicycle, but I didn't notice concussion symptoms until the next day. I did not feel "clear headed" for almost a year afterwards. Concussions are horrible, terrifying things. Maybe the worst part is, the damage from concussions does not fully heal, and it tends to accumulate over time. I feel bad for Joe Mauer. His symptoms may fade, but he will be vulnerable to concussion symptoms for the rest of his life.