Start with what you are eating and drinking - especially drinking. If you are drinking large amounts of caffeine, alcohol, and possibly even dairy could be an issue for you.
It could also be a deficiency from NOT eating something.
It could also be from any sports you have been playing over the past few years. Any team sport involves a certain amount of contact. Even if you have not had a concussion, you could still have some neurological sub-consussive injury.