Does fibromyalgia exist? Tension headaches? What about chronic fatigue or irritable bowel syndrome? How are they diagnosed?

Pain is a symptom of all those diseases, which is why is said "Pain is a symptom not a disease"

Yet the threshold is vague and arbitrary

Whats that got to do with clumsiness and forgetfulness being a disease?

They are all subjective, arbitrary, "not observable", "in the mind", "not objective"