What have I injured here?

I did a somersault yesterday and put too much effort in and misjudged the landing. As a result I landed with my legs straight instead of bent. It hurt my neck, but not anything else.

I ended up with a sore neck and a headache. It’s now the next morning and I have a headache. I’m really not at all familiar with the make up of this part of the body. So, my question is: What did I do to myself, what have I injured? I would have expected my back and my knees to hurt, but no.

Now, before anyone whinges at my to go to the doctor, I’m going to go tomorrow if my head still hurts, ok!?