Disapointed to hear your comment .18 months ago I had a delayed reaction to thunderstorm asthma and was unable to breathe at night. First I sat up and walked around, but it got worse and found it impossible to breathe at night. I went to hospital and after several tests, I had to do a further examination and then recommended for more heart surgery. In the meantime my cardiologist in the same hospital was aghast. You will not survive if you do this operation and looked for alternatives. Eventually there was no alternative and we confirmed the operation. I updated my will and instructions to my executor and paid up all outstanding accounts.
I survived and my instructions in long term rehab was to include a 2 kilo walk each day regardless of pace at first.
That was in June 2017 and I have had 4 trips to Thailand since. The walking on Pattaya footpaths is not even and pleasant and I went backwards.
My friend suggested walking DOWN the fire escape . I have gone from one floor to seven floors and have increased to three trips each day on this last trip. I am now 82 and now have more zing in my movements, and next trip will try to increase each trip to ten floors.
Can I urge you to reconsider your stair walking and try again.
My friend 25 year younger who is receiving physio work for damaged neck and shoulder, had similar problems. He is probably an even worse swimmer than you. He remembers the Life Saving marchpasts than he used to watch on our beaches. He loved the tight and revealing speedos.
He was cooling off in the pool and remembered the march past where Lifesavers lifted the knees to waist high.
It was just a thought and he found himself exhausted from two marches crosspool in the water.
In a recent email he said his target was 10 crossings with a total of 300 lifts. Does in his own time and increases a little at a time.
I have just returned home as the monson rains seem to be coming more frequent. If you do not like walking[running] in the rain, maybe these ideas may help.