Dr Myhill is a well known name amongst the CFS/ME community thanks to her book "It's mitochondria not hypochondria" which talks about some of the physical causes of the condition. She presents the science behind the theory that those with CFS don't have properly functioning mitochondria, which leads to us being unable to produce energy properly.
Personally, I never had mine measured as it was too expensive and Dr Myhill can only take on a certain number of patients at any one time. But, I did follow a lot of the advice she recommends - changes to diet and taking a number of different supplements which my body needs in order to produce energy. This made a big difference to my health, it was a turning point in my recovery combined with the hydrotherapy I was offered. I'm very much of the opinion that what works for one person may not work for everyone, but this was something I could try without fearing I'd do further damage. I don't follow it strictly anymore although if I'm crashing I do to help me recover faster.