I hit my head on the tailgate of our car. Just walked into it at normal walking speed, but it was hard enough that i felt immediately dizzy. I did not pass out, just knelt to the ground and got up after a minute. I kept doing house work after that and feel largely OK, but my head feels heavy and it hurts a little (in general, not at the spot I hit). Not terrible pain, it s just that I notice it. Do I need to go to the ER, or can I monitor for a while and look for additional symptoms. If so, what should I look for.