Hope this is in the right place.

Hi,
For several years, whenever I do something enjoyable (even something as simple as reading something that interests me online), my body automatically tenses a few times really quickly. It's not in any one area, just my whole body. It doesn't seem controllable, but for some reason it's only when I'm enjoying something. Sometimes it causes a slight headache, neck pain, or lightheadedness. I feel like a freak because this is such a weird thing. I imagine it's sort of like a nervous tick, but why is it not when I'm nervous? ANY IDEAS? :(