Hi Gm,
I think I know what you mean - it's like a irrational thought is placed in your head when you are doing something that is supposed to be enjoyable, or at least neutral, and then that thought grows till you realise that you have stopped enjoying what you are doing and it becomes a tiresome effort. That's what it's like for me anyway.
Firstly, good idea by describing the physical symptoms (i.e. the heaviness in your chest). You can practice managing the physiological changes that the intrusive thoughts create by doing things like slow, deep breathing. Exercise helps a lot as well.
^That stuff I learned from a psychologist.
On a deeper level, why are those thoughts intrusive and are they rational (if not, are they worthy of your mental energy)?
I'll give you an example (albeit a simplistic one).
Yesterday I was playing footy. Usually I'm pretty good at kicking, but all of a sudden I had one bad kick and a process of thoughts ignited in my brain - "that was terrible", "you've never been a good kick", "remember all those times when you stuffed up your kicking", "you are a failure". I was scared of kicking for the rest of the game (I even gave a few goals away because of it!).
I remember really looking forward to playing before the game and not enjoying it after my (single) negative experience. It felt like it ruined the fun for me.
Looking back on it now I can see how silly of me it was to think that way. There were loads of positive experiences that the game provided, yet I neglected them because they did not conform to my (problematic) belief that "I am a failure".
In your case, it might be helpful to look at what belief your thoughts are conforming to, and whether or not the evidence you have actually supports that belief.
^That stuff I learned from Cognitive Behaviour Therapy (CBT) which was provided by a psychologist.
Heres a CBT package for Generalised Anxiety that I found very helfpul: http://www.cci.health.wa.gov.au/resources/infopax.cfm?Info_ID=46
Hope I could be of some service,
Ben
