From thinkfirst.ca:

"The best medical management for a concussion is rest, both physical and mental. A person who has suffered a concussion may often feel lethargic and tired. It is important to admit this fatigue to yourself. Your brain is telling you that you need rest and it is extremely important that you listen to it. If you continue pushing yourself and struggling on, it is likely you will make the symptoms worse."

http://www.thinkfirst.ca/programs/concussionqanda.aspx