It sounds like you are having lots of panic
attacks, and these
in turn are causing
the fast
heart rate and
the flutters. You probably notice them more when you are sitting due to the fact that you are not doing anything to distract yourself, and sometimes, the heart will calm down when you are walking, etc.
I have anxiety attacks, and it is a vicious circle, the more I worry, the more heart flutters, I feel, the more heart flutters I feel, the more anxious I get, ugh, it is awful.