OK, so what is it then? I've had this for years and found no explanation so far.
Does anyone else experience this? It's like I need to "turn off the world" every now and then in order to be able to continue.
PS: some nausea is also usually present at that point.
It sounds like it might be related to dysautonomia. Since many people with ME (PWME) have dysautonomia, your episode could be related to ME, but it might also be dysautonomia from some other source, or primary dysautonomia.
If you are having an orthostatic intolerance (OI) problem during these episodes, that might explain the difficulty thinking (poor blood flow to the brain), and nausea (common with low BP). Cold hands can be from poor blood flow or poor body temperature control as a result of dysautonomia.
A useful investigation would be to check your BP and HR when you feel rotten, but before you lie down, after you've been lying down for a while, and once again after you feel better. You might find
this PR article on orthostatic intolerance helpful, especially the section on diagnosis. Dysautonomia can be much more than just OI, and OI can be much more than POTS, although few doctors understand this. It's a specialist field that many doctors think they know more about than they do.
The good news, if there is such a thing with this illness, is that there are treatments that can help with OI, so if that's what you're experiencing, there's hope you can reduce the magnitude or frequency of these episodes.
In my experience, a PEM/PENE-type crash is more severe, lasts longer, and has more flu-like symptoms. It is usually delayed (although not always) and has a delayed recovery. I believe the definitions require recovery to take a
minimum of 24 hrs.