Suggest Treatment For Head Injury

I hit my head very hard about an hour ago, hard enough I fell backwards onto my rear and there is a slight scrape/cut that bled a little. The area is very tender and I put ice on it. I am not sure if I should go to the ER or not, as I hit it very hard and can't remember if I possibly blacked out for a second or two, or was just stunned. Should I go to the ER?