Before engaging in any Graded Exercise Therapy (GET) please get your therapist to watch this 20 minute video that explains why working up to walking for a targeted amount of time does not necessarily make you healthier or more functional even if you reach said target, and how this type of therapy can actually undermine your health even though you're walking more than you were before implementing GET.
There is some epidemiological evidence as to GET failing ME/CFS and FM patients, but here is a great physiological explanation to give to your health care team as to why people with ME/CFS/FM need to take great care implementing any new exercise program. It also explains the mechanism behind why you should never be pushed beyond your limit, and often not even to your limit.
Exercise physiologist Staci Stevens explains this phenomenon that ME/CFS and FM patients all face and gives tips on how to effectively manage exercise intolerance.
The tinny sound goes away after a few minutes.