Some of the Why's:

Here are just a few of the Why's I've found answers to, which I'm sharing for anyone who has these conditions or think they may have them, or knows someone with them, or are simply interested. This is very brief -- I intend to gather more of the information and research that has been most helpful for me into a more cohesive format, but for now...

• Why am I excessively tired, ache all over, and unable to manage nearly as much as I used to, way less even than the average person twenty years my senior? It's fibromyalgia and ME, not laziness and apathy fueled by a morbid imagination. HealthRising.org is a invaluably informative website for both these conditions.
• Why can I feel full of beans one morning like I could go all day yet by afternoon be flattened by fatigue that lasts for the half a week? ME involves a problem with the body's mitochondrial ATP energy production process, with less energy generated one becomes fatigued much quicker and it takes much longer to recover from any physical and mental exertion.
• Why I am I so much more sensitive to touch, sound and light? In FM there's an increase in neurotransmitters  involved in regulation of the pain threshold, the point at which sensation is perceived as pain, so my brain is experiencing sensations at a much greater intensity.
• Why does it take exponentially more effort for me to perform similar activities a few days in a row?  (I'm talking about simple things, like a gentle walk, which should actually enhance energy production.) Although people with ME can physiologically push themselves to repeat an activity they managed the previous day, their bodies are unable to replicate the same amount of power output and they can also struggle to get their heart rate up enough. (Why the low heart rate? It's not due to cardiac problems, but related to low active thyroid hormone T3 which controls the body's metabolism. Why low T3?  It's not a thyroid problem because my thyroid is creating plenty of inactive thyroid hormone T4. However it's not being converted to active T3 (conversion occurs primarily in the liver and also the gut) and instead being converted to reverse T3, which slows metabolism. Why does the body convert T4 to reverseT3 instead of T3? To conserve energy, for instance during emotional, physical, or biological stress, such as being chronically or acutely sick, after surgery, a car accident or any acute injury, chronic stress, etc. And then off down that rabbit hole you go!)
• Why do I and others with ME and FM not look sick? That's an interesting one. These are not visible conditions with obvious appearance like bruises or broken bones. What does fatigue and pain look like? That's like asking what a broken heart looks like. Physiologically, possibly due to the hibernation-like state of our mitochondria which causes all metabolic processes to slow down, the natural degenerative processes are not happening as fast they would otherwise. I'd rather look twice my age than feel twice my age, but at least it's a nice side-effect. In any case, you'll rarely see us when we're not feeling strong enough to be up and about.
• Why was I feeling so much better two years ago, yet now have ME as well as fibroyalgia?  Stress in any form, be it physical, cognitive, emotional, environmental, places an additional load on any system. Although I had reached the point where I had recovered sufficient health to be living a more regular life again, I had no reserves for additional stress, so when I experienced a rather terrifying situation followed by a prolonged stressful period, all my energy was required just to cope. Many ME patients start out with FM and devolve into ME/FM as their energy levels decline. As cellular energy is depleted, fatigue and muscle pain become more and more severe, and the muscles require additional energy in their recovery efforts. Energy is used faster than fuel is made available to renew it, and the fatigue, soreness, pain and stiffness continue to progress. Energy depletion reaches a critical point, and ME/FM becomes a state in which the mechanisms for recovery are overwhelmed.
• Why do symptomatic pharmaceutical treatments that help in other condition not help for ME and FM and often cause really nasty side effects? Because the root cause of the symptoms in ME and FM is not the same root cause of conditions like depression, arthritis, etc . Since clinical trials have so far failed to provide overall benefits without associated harms, current pharmacological treatments are merely symptom palliative. Polypharmacy often leads to patient’s health deterioration and chronic drug use to an eventual lack of patient’s response.
• Why do bodywork treatments like fascia release have such noticeable benefits? The fascia is a continuous network of web-like connective tissue running throughout our body and plays a key role in generating the pain and muscle tenderness of fibromyalgia. The fascia contains lots of pain-sensing nerves and is about as sensitive to pain as our skin. It is the connective tissue “armor” of the body, tightening immediately in response to signals from the many nerves running throughout it. This provides strength in emergency situations and can be life-saving in the short-term. In fibromyalgia we know that the brain is mistakenly triggering the danger or “fight-or-flight” alarm bells all the time, instead of only in emergencies. This occurs not in our thinking brain, but in those areas that control basic housekeeping functions like breathing and digestion. As research advances, we are learning that the tightness lies not only in the muscles themselves but also in the fascia, and this sustained tightness of the fascia not only causes pain, it also generates inflammation, and contorts the muscles into painful knots called trigger points.
• Why do I have these conditions in the first place? No definite answers to that yet, although there's some good research happening and it is believed to involve a combination of genetic and environmental factors.