A direct hit to the head is almost always worse than a glancing blow due to blunt force trauma. Its physics and the transfer of shock of impact to the brain which leads to brain contusions and other injuries causing many concussions. I don't claim to be an expert on the subject matter but i do know quite a bit based on my own experiences with it. The point is they are difficult to predict but there are some known facts out there. Morneau's concussion was far worse than Mauer's which is why it took him so much longer to come back. I also think his lingering symptoms (nausea, dizziness, etc.) were much worse than Mauer's vision issues. About 30-65% of people with TBI have issues with balance, dizziness, visual distortions, etc., depending on the severity of the concussion. A smaller percentage of that number has permanent issues such as vertigo. I would hope that Mauer would have communicated these issues to the Twins training staff promptly instead of waiting several years as he claims. I don't want to get into the Twins medical staff was awful so he tried to go it alone blah blah blah as Deduno Abides states. That is all pure speculation.