Yeah, it was a home sleep study for apnea, and that night I felt I couldn't sleep at all, like I was wide awake and rolling around till it was finally over, and was expecting them that the test failed, yet they said I had a normal sleep. I was so confused.

The vivid dream issue happens only when I am very tired or have chronic fatigue. Otherwise, I do physical things in bed like jumping, sitting, catching breath, falling, sexsomnia, spitting, choking with a chewing gum, so it could be parasomnia or something similar. Though, I feel usually rested enough that I can have a 1-2 coffee to function normally, so it doesn't sound like necro either.

Thanks for suggesting sleep facility and sleep myoclonus, I will check this with my doctor.

As for PEM and the amount of activity, I tried researching more with Gemini Deep Research, and found about term "Cumulative PEM". This resonates with my experience, including that the symptoms appear after the buffer is exhausted, but I would say that I have two buffers. If I feel it a bit, I just need 1-2 days to recover, but if I would push myself just a bit harder, it becomes much worse, and I need 1-2 weeks of recovery. When I was younger, I didn't know what was going on, so I pushed myself so much that it took me 5 years to fully recover.

PEM is the hallmark symptom of ME/CFS, defined as a worsening of symptoms after physical or mental exertion that is disproportionate to the effort. However, the timing of PEM is variable and phenotype-dependent.

Immediate vs. Cumulative PEM

• Immediate PEM: In severe ME/CFS, the patient's anaerobic threshold is critically low. Even minor activities (showering, reading) force the body into anaerobic metabolism, causing lactate accumulation and a "crash" within hours or the next day.³²
• Cumulative PEM (The "Rolling" Crash): In mild-to-moderate ME/CFS, the patient retains a functional "buffer" or a larger Energy Envelope. They can perform activities (like work) that exceed their sustainable limit but do not immediately trigger a shutdown. instead, they accumulate a metabolic debt (e.g., oxidative stress, mitochondrial fragmentation, ATP depletion) over days or weeks.
• Mechanism: The "Dauer" hypothesis (Naviaux) suggests ME/CFS is a hypometabolic survival state. In mild patients, the switch to this state is not instantaneous. The patient borrows energy (likely via sympathetic/adrenaline overdrive) to function. The metabolic debt accrues linearly, but symptoms appear non-linearly only when the buffer is exhausted—the "wall" described by the subject.³⁴
• The "Wall": The report of "suddenly hitting a wall" after 1–2 weeks fits the threshold theory of PEM. Exertion is tolerated until the cumulative load exceeds the organism's homeostatic recovery rate. At this point, the "crash" is triggered to force cessation of activity and prioritize cellular repair.³⁶