Hi - this is my first time here - I keep having this weird sensation of 'sinking' in my chest - it's like everything in there is kind of sinking down towards my stomach. I get kind of shallow breathing and I feel really, really tired and veryweak. It passes - sometimes after half an hour sometimes a bit more and it's always so far happened when I've been outside walking. I've got a lot of stressful things going on in my life at the moment - my own feeling is that it's related to this as it doesn't get worse if I continue walking and I'm usually quite fit and active. Also, I think I make it worse when it comes on by worrying about it. It just comes and goes when it feels like it. I can walk up a steep hill for half an hour without feeling bothered. Any ideas? Thanks for reading this.