Yes. Something called “post exertional malaise” which can be tested via the Stevens Protocol. In short, given the same exercise test two days in a row, normal

Yes. Something called “post exertional malaise” which can be tested via the Stevens Protocol. In short, given the same exercise test two days in a row, normal people behave the same (slightly better even) but CFS patients degrade substantially. A variety of other tests such as tilt table tests, Cardio Pulmonary Exercise Tests (CPET) and Advanced Invasive CPET are also able to diagnose physical symptoms, and sometimes even treatable sub-sets of the condition.