After 50 years plus of smoking I have some breathing issues and may have COPD.  I quit the smokes almost 12 years ago but my breathing isn't as good as I'd like.  I keep coughing up muck and suffer shortness of breath on occasion.  At last check in with my doctor I was cleared of any growths on my lungs or emphysema, so I'm not too worried about cancer, etc.  However, I should go and get checked again to find out why I have all this muck on my chest and what to do about it.
I know that doing more exercise would help, and I'm looking into that with my doctor and a physiotherapist.  I need to be able to do low impact exercises that are kind to my poor old arthritic bones, but exercises that help to improve my cardio-vascular and lung capacity.
Anyhow, Ross, I know how you feel and hope you are on the mend.  Get well soon my friend.
Oh, and quitting the smokes was the best thing I ever did for my health... and wallet.  Before I quit I had to stop several times when mowing the lawns, and my breathing was quite laboured most of the time.  Now I can mow the lawns in one go and my breathing has improved considerably.  So yeah, I mightn't be 100% just yet, but I'm definitely much better off for quitting.