P-PEM for me means irregular heartbeat, chills, hypotension episodes and then EVENTUALLY (24-48 hours later) weakness, cognitive problems, irritability, confusion.
M-PEM for me means same cognitive problems but right away, without delay, and often accompanied by headache which is not a P-PEM symptom for me.
I think the cognitive type of PEM is the same for both P and M, but the process of getting there feels very different.
I should add that long phases of overdoing it, on the other hand, have their own symptom complex. This is when the sore throats, fevers, puffy glands and general SICK feeling come into play. This will come from both mental and physical exertion with no clear difference. This is what happens if I push through the initial P- or M- PEM to do something I want to or need to do regardless of how I feel.