I believe that our very low energy levels are in part caused by our bodies safety mechanisms trying to protect us against bad accumulating permanent damage. Producing energy does produce waste. If our bodies are disregulated, IMO that waste can pile up quickly even when doing only modest activities.
Many things can be at the basis. Chronic infections, poor genes largely blocking key biochemical processes in combination with reduced spare capacity to work around it by aging, heavy metal poisoning, gut imbalance and many more including a wrong safety mechanism. That can be the case too, but personnaly I feel in 90+% of cases there likely has to be an underlying weakness rightfully triggering those safeties.
Many people experience something similar in the comment section of Cort's recent blog
https://www.healthrising.org/blog/2020/11/19/coq10-fibromyalgia-chronic-fatigue-syndrome-review/:
When taking a new drug or supplement it works for 1 to 2 days and then it stops working or they even get worse. It seems to be *very* common. It's very interesting to sort through that comment section and see people talking about their experiences.
In my case the same even happens when I *quit* taking a drug:
I take a new drug, I feel better for 1 to 2 days. Then nothing or side effects for a long time. When I quit the drug, I often feel better for another single day again and then that is gone too.
=> I believe the safety mechanisms of our body try and protect us against permanent damage piling up quickly if we would use and produce energy like usual because of some individually different underlying though health issues. The easiest way to protect us against massive accumulating permanent damage (MS, Parkinson or Alzheimer Disease style) in *our* case may be our bodies *doing active effort* to inhibit energy production and depress our mood and willpower to overexert.
For doing that, it has to operate our body outside its usual parameters and procedures to "optimally inhibit and protect us". When something disturbs that equilibrum, like taking or even quiting a new drug, taking new supplements or getting a sudden modest infection, the body might be taken off guard and unable "to optimally inhibit" our energy production in order to optimally protect us against long term bad permanent damage. If that idea is close, it seems to take 1 to 2 days for it to find a new "sick" balance for plenty of ME patients.