Chronic fatigue and the problem with deconditioning

Here's my graphical attempt to explain it.

This seems to be what is happening with me.

 We start out with some underlying illness that knocks us for six. It lasts for a long time. We try to deal with it but we can't, and so we reduce our activity (to very little). We become physically deconditioned. Perhaps the illness wears off (there is no way of measuring this unfortunately - although my immune system blood tests are still wonky), but we still feel ill for two other reasons:

 - we are completely deconditioned and any effort triggers exhaustion symptoms
 - we have become psychologically habituated to our illness response at a very deep level

 And the nightmare continues. The illness feels almost the same as it always did, (perhaps we get signs that we can do more) and we struggle on. This occurs over years.

 My main point is this: it is tremendously difficult.