Anxiety

Dear Dr: Even though I feel healthy, why is it that I feel terrible after doing physical work. I'm 62 and quite fit; in fact I can walk all day, but when I start to do some work around the house or garden, I feel as if I am breathing my last breath. I was checked by a Physician and my heart is fine.....what gives? (ps) I was in the grips of anxiety for 10 years, but seem to be coming out of it .....thank you