Yes I agree Peter. Everything about
this disease is 'a bit more complicated'.
I wanted to come up with a really simple explanation. The 'normally closed' valve goes, and you are left with only the 'normally
open' valve, which has to re-learn its job with the aid of stronger muscles. This is a big change, losing your main valve and having to rely only on a secondary valve, and one that needs to re-configure its operation. (And no back-up any longer.)
The terms I use have specific meaning to the more technically-minded people here, but I think makes perfect sense in plain English too. A few people whom I know struggled to understand what is happening to them, but understood it once I used this (somewhat simplified) explanation.
You will get there. Keep believing.