Could it be a Concussion?

I am not worried, just curious. I was playing with my dog, a boxer/lab mix, and I threw a tennis ball for her at close range and when she tried to catch it she bounced it back and it hit me right in the forehead. I don't think it hit hard enough to cause any real damage, it may or may not bruise

I was already tired before but afterward I felt and feel more tired, everything is funny and I am only a tiny bit dizzy. So my question is, could that be enough to cause a minor concussion?