Does anyone ever feel... bad... but don't know why? (I mean physically)

Body-wise, I was feeling weird when I had a sudden burst of energy and "heart flutters" and that may already be the answer to my question as to what was ailing me or what I felt physically "bad."

Thing is, I couldn't tell you otherwise what was bad and why my mood dropped when my energy rose.

It may be that, when I get energy, I feel angst or anguish over realizing the state of things as my mind becomes clear or perhaps I'm feeling my own body or lack of depersonalization for the first time (it's happened multiple times but you know what I mean).

I don't want to be unscientific so I thought I'd ask others here with the hopes that someone will have the valid answer (of course, I'm using Google or Bing so it's not like I'm just relying on the opinion of random people, though maybe the search results aren't that good either).