I haven't found a better single word or short phrase to describe PEM, but I agree malaise is not perfect.
The problems for me are:
I have malaise all the time - feeling ill, aching/painful muscles, drained exhausted feeling, sometimes headache, sore throat, nausea, IBS symptoms OI, physical and cognitive fatiguablity, etc. All the usual stuff we know so well.
I also have severely limited function all the time.
So I need something that indicates that PEM is different.
All my symptoms much worse,
Extra symptoms that I don't have all the time, like dizziness, vomiting, headache, loss of appetite, bedbound, unable to think, concentrate or talk coherently ...
and much more severely limited function.
PESE, post exertional symptom exacerbation, is being used more often, including as an alternative in the new NICE guidelines.
I don't particularly like it, because it's too easily interpreted, in the context of the name 'Chronic fatigue syndrome' to mean post exertional increase in fatigue.
I think we have to accept that no term will be perfect. I would like one that combines:
- disabling and unpleasant symptoms that are ever present becoming significantly worse
- additional symptoms
- significantly reduced function
- usually delayed onset, and duration more, and sometimes much more, than 24 hours
I think that's why many of us use the term 'crash'. It seems to convey, though in lay rather than medical terms, something significantly awful and disabling.