Is it 'only' a mild concussion?
Concussions are an ever-present possibility in grappling, especially if you do a lot of takedowns or striking. In fact I think it’s fair to say that everyone training in a combat sport for long enough will get hit on the head hard enough at some point to have some kind of concussion.
Of course we all try to be careful and minimize the risk, but the possibility of a concussion is just the price of admission for being a serious student of the martial arts.
But knowledge is power, and this article on post-concussion syndrome is worth reading just in case you, or someone you know, suffers from headaches, dizziness and trouble concentrating after a blow to the head.