I have to say first off I agree with the other posters that you need to be seeking either another opinion about your treatment or you need to be on some form of meds - 20% drop in FEV1 is huge over a 2 yr period especially if you have not bene given any treatment to help correct the problem.
On the the question you asked.
For me before I was transplanted my lung function was at about 23% FEV1 and pretty much everything was hard. When I was sick - which was often - my FEV1 would drop into the teens maybe 18-19%. Getting up the energy to take a shower was a task and walking was difficult and if I had to carry something it at times felt impossible.
When my lung function was in the mid 30% range for FEV1 things were more tolerable but still very hard. I was able to do most things but became VERY short of breath with them and it took me longer to do most things as well. I definitely moved at a slower pace than most everyone.
The 40% range is where I started to notice a big difference in my activity level and ability. I started slowing down at this point. My energy level decreased and my abilities became more limited. I still was able to push through most things, but at this point is when my body started to really weaken I think.
When I was above 50%, and in the 60% range even, I did not notice much of a difference except when I would run. I could jog some but always tired quickly. I could sprint for VERY short distances but became breatheless very fast. Also I started at this point having a VERY difficult time maintaining any muscle mass or even building muscle mass.
I do not remember much of anything when I had lung function higher than 65% with CF lungs. I was probably around the age of 10 when my lung function was higher than that - so sorry I can not help much there.
As for now - just over 2 months post transplant - my lung function on last measure was about 75% FEV1. I am able to do most things with ease. I find now the hardest part for me is dealing with how deconditioned I was before transplant. My lack of muscle is more of the problem now - my body can not keep up with my lungs, where before my body had to slow down for my lungs. I have to build my muscle and strength up too meet the capacity and ability my new lungs are affording me.
I sit in amazement at the improvement and am just in awe of the ability we as CFers have to push ourselves at such low numbers. Especially since my increase in lung function occurred in about a 2 week period - I went from 22% FEV1 pre transplant to about 50% FEV1 2 weeks post and now 75% 2 months post; it is more obvious to me the difference NOW than it was before because the decline happened so gradually.
Well I will end this now but yeah I hope that maybe answered your question.
Take Care,
Lindsey