What Causes Dizziness And Dull Pain After Having Fallen On Buttocks On Beach?

About 12 hours ago, I was walking on the sandy beach, and fell on my butt, backwards. Immediately, I felt the left side of my head hurting with dull pain. Only about 5 minutes later it left completely. However, this morning I awoke feeling dizzy with the room spinning, as I lie in bed, and after standing up, dizziness left. Of course, I'm a little worried, and wonder if that had anything to do with the dizziness. I appreciate your insight.