I got a concussion during the second semester of my freshman year and I am not necessarily promoting staying in school, but I did and I just graduated. My GPA dropped by .8 but it taught me a lot about the kindness of other people and asking for help without being helpless.
For me, especially at the beginning, I would ask different classmates to sum up what the chapter was about or one friend even read the homework out loud to me because the light sensitivity was so bad that I had to close my eyes. I have read of other people dictating their essays to friends who were really fast typists. During class make sure that you highlight and underline and take notes summarizing what is being said and the meaning of the text assigned. Also, weekends are for sleep and study not partying. You can pay your friends back for all they help by giving them your insight into what they have been helping you with. Also, for them they have to look over it twice, or at least more slowly so you are helping them to study too. Create study groups with several people all discussing the material and then you sit and listen and take notes. Don't be afraid to let people know what you are going through. People love to help other people who seem like they are trying. If you are going to go do something relaxing on the weekends, make sure that it is relaxing for your brain. I always liked watching movies or playing cards.
Tell your professors what is going on and also tell the dean of your college. They can then maybe give you longer times on exams. Also set up meetings with your professors to discuss the material in private. Let them know what you are going through and ask if there is a general outline that you can study to help you focus your efforts.
Most of all be honest. If you ask for help make sure that you show an honest effort and that they don't see you staggering out drunk from the latest frat party. And if they tell you not to share the info they give you, don't.

I suffered 2 concussions about 2 weeks apart during my second semester freshman year in college. I took between 18 and 23 credit hours per semester. I slept 7 hours a night and was known for being a little aloof or distant because I wouldn't go to the big parties. My closest friends changed the way that we had fun so that we could all do it together. It is 4 years later and I still am suffering from daily headaches. I have bumped my head many more times at least 12 times were serious bumps and at least 4 of those I think were concussions. I have been to see at least 10 different doctors who all say that they can't help me. The best medicine I can recommend is to find that one person who you can tell everything about how awful your day is going and then you can move on and do other fun things with that person. This contact person helps you to spill it all out and then go out to stare at the stars despite your pain and whatever else. For me this friend was a person who suffered from chronic migraines and had never had a concussion. But we had similar issues and had similar disabilities, meaning we could or couldn't do about the same level of activities. This is a friendship that I think will last until I die, and we bonded over pain.

Anyways, good luck! There is a light at the end of the tunnel and that light says that you have a college degree despite it all and you have friendships that helped to make that happen. You will come out a much more disciplined and stronger person, and many people will be impressed even if they do not know the reasons why. Also without that degree think about the kind of depressing jobs you can get, whereas with that degree you can do something so exciting that it will help to distract you from the injury.

I have gone on for too long.
Live Long and Prosper!
In Christ,
Margarite