What I want to say is this:

It seems perfectly feasible that AOS may be the cause of my symptoms. What I do not get is why this is classified as a functional disorder.

As far as I (did) understand, the argument for having a 'functional' disorder was that the cause was emotional and/or behavioural. Now, IF I have AOS, the argument goes I have a dysfunctional relationship with exercise and eating that has caused me to have physical repercussions.

If a patient who over-eats and has high cholesterol ultimately has a heart attack, does that mean the illness is 'functional'? Over-eating is, arguably, a behavioural problem. This doesn't mean (as I would argue in my case) that the over-eating/over-exercising is deliberate, it just means it's lead to the consequent physical illness. So what's the difference?

I don't 'buy into' the use of the word 'functional' and never have. The fact that there are varied opinions on what this means between physicians makes me very confused. Let me give you an example:

The neurologist who arranged for my admission said my illness was caused by an 'emotional problem' (he included ME in this category).
The neurologist who assessed me on admission told me my illness was caused by a virus.
The doctor who assessed me after admission told me that my illness was caused by back injury.

All three explanations are classed as 'functional'. This means perhaps I have misunderstood the meaning of the term. If my illness is caused by a virus, it's not caused by an 'emotional problem', which seemed to me to be the justification for it being 'functional'. If AOS is a neuro-endocrine disorder, and I have been suffering the symptoms of untreated hypoglycemia for the last three years, why is that 'functional'? Because the cause of it was 'behavioural' in the sense I inadvertently, on a few occasions, took a lot of exercise, and due to circumstance, failed to meet calorific requirements?