I think it is very confusing. Undoubtedly not everyone with ME/CFS has POTS but for me it developed after about 5 years of having ME/CFS though I think I might have had a slightly milder version of it from the start because the heart racing/dizziness, coming out of nowhere goes back a long time but I think it has changed as time has gone by and now definitely there is the uncontrolled sweating, dizziness, feelings of anxiety and wanting to sit down or preferably lie down and rest. Then I am aware that my legs have gone very stiff and could do with a massage but I wouldn't have the energy to do that, at least not until I have breathed my oxygen concentrator for at least 30 minutes plus I feel exhaustion.
BTW I was tested at the Breakspear private hospital here in the UK for Autonomic Function and this is where they found I had less than 50% of normal values of oxygen in my cells hence their recommendation that I needed to breathe oxygen at least 3 times daily. It has made a massive difference to what I can achieve each day. I think this develops over time because I definitely didn't need it 10 years ago. During the test on that day I had above normal levels of Carbon Dioxide.
I also have problems with very frequent sore throats, in fact it never looks normal. Also I have 5 or 6 raised antibodies to different Herpes type viruses so again this is typical of ME/CFS.
But one very important difference with me to most sufferers is that I feel better for exercise every day unless I have an infection. I can only manage around 20 - 30 minutes maximum of walking at a good pace but if I don't do this my whole body feels worse, very achy and sore plus my brain feels sluggish and not happy. It was like this today when I did work on my laptop for a good part of the morning and then took some friends out at dinnertime which lasted 2 1/2 hours. Then I went back for a cup of tea to one of the friend's flats so was sitting around yet again. I got home after 4 hours feeling drained and tired. I used my concentrator and soon fell asleep for 25 minutes and felt much better after.
However my legs felt horrible, achy and not right so I went for a good 20 minutes walk around the block in the dark despite it being cold and windy. Once back I felt so much better, mood improved and somehow my body just feels happier. Now I know that is not typical of ME/CFS. If I was to overdo the walking then I would definitely feel very bad but the POTS would have kicked in big time so is that the reason I would feel so bad?
I have to take a daily, replacement dose of steroid, ie 6mg Prednisolone which enables me to take thyroid medication because I have Hashimotos. Both of these would support my body, certainly not curing me but I wonder if this is the reason why I am able and want to exercise daily? Its all so complicated and way beyond my GP!
Pam