It could be caused by a multitude of different maladies, as it can manifest in many different shapes and forms, aches and pains, aversions and limitations, but the primary symptom is persistent, debilitating fatigue. For me it has been weirdly comforting to read of others symptoms on the internet - I guess it validates my experience, and makes me feel like I'm not just weird, alone and making this stuff up in my head. So to describe my own experience, here are some metaphors and similes, accompanied with some dodgy finger drawings done on an iPad.
The first and foremost point is it is not a healthy 'had a big day' tired. Its a sick tired. The tired that you get with the flu.
Interestingly, I think my first symptom this year was that I rather suddenly became a mega introvert. I felt an painful aversion to interacting with people. I just wanted to hide and protect myself and I could feel really strongly how interacting some people drained my energy. (However my previous episodes of fatigue did not affect my social energy, only physical.)
In my last episode of fatigue, my first symptom was an aversion to what is usually one of my favourite things: cold water swimming. Being cold nowadays is a very unattractive idea.
When I'm healthy, exercise gives me energy and endorphins, like the alternator in the car recharges the battery when you drive it. I usually need exercise to feel good physically and mentally. When I have fatigue, exercise just drains out my energy without recharging it. Its like I have a broken alternator.
Or maybe its like I have a leak in my energy fuel tank that drains out as fast as I fill it.
Or perhaps the pipe from which 'energy' comes from is blocked and its only dripping through very slowly into the fuel tank. I need to rest for a long time after exertion to fill up again.
Or I have really cheap, low quality batteries. They indicate they are fully charged, but a few minutes into a gentle walk, they are suddenly empty, I am exhausted and the distance to get home has become very long.
Sometimes I can be quite wired, as my body relies on adrenaline rather than 'proper' energy to get things done. This can make winding down hard, and sleep unrefreshing. I wake up groggy and sluggish. Luckily this time I have been sleeping well, but last year I got a dose of the 'wired and tired'.
Last time I got better in a linear fashion, but during this latest recurrence Ive stumbled upon a lot more falls and setbacks along the way. Its like I've fallen some of the way down a very deep hole. Its a long way up. I don't know how deep the hole is and it is scary to think. The only way out is to feel my way very very carefully, taking very very slow steps. If I rush I may lose my grip, or cause the walls to crumble, and I could tumble and crash even deeper. I'm on a precarious ledge and I'm finding my way by touch. How much I keep trying to climb out, and how much I am patient and wait, is a constant dilemma.
But sometimes when I am waiting there are nice things like butterflies to look at.
And the truth is, as I can't really see my way around down here, I don't actually know what the terrain is like above or below me. It could get worse. It could also get better. And the internet also tells me that, while there is no silver bullet,
(I have enjoyed and found inspiration from listening to the collection of audio interviews with cfs recoverees, on Dan Neuffer's website "CFS unravelled".)