I think its what your eating and not.

Also I think its in our blood to feel it. We are humans/animals. We had stress when we were hunters in short moments (when we had to run away from a lion or hunting a mammoth)

Now we don't have any of that in our life, our mind needs it to feel like its doing its job. Its normal I believe. When you are feeling that way, you will be amazed at going out for a run, bike ride, work out with weights, your mood will change.

But just put those feelings to use.