What happens if you hit your head on the ground really hard?

I like to do extreme things like Parkour, Free Running and Martial Arts Tricking, so I'm always jumping around. About 3 weeks ago I decided to go outside and try a new back flip, but it had just rained and when I went for the flip it was high and quick. Unfortunatley I slipped on the wet grass and fell back and hit my head on the grass. I quickly stood up and felt dizzy and I could feel a bunch of blood rushing to my head. I stayed up to make sure nothing was wrong, but I was so tired that I fell asleep and woke up a few hours later. Then, 2 weeks later I got sick and had headaches, and now my sickness is almost completely gone but I still have mild headaches, especially when I cough or am outside flipping. I've been thinking about going to the doctor to check it out but it could just be a symptom from having the flu. Does anyone have any suggestions on what I should do?