@gettinbetter this is very familiar and something that started long before I got CFS/ME.
I am a migrainer whose migraines are triggered by glare and pattern glare: flourescent lightning is probably the most common source of pattern glare.
When I was a teenager going to school in flourescently lit classrooms I sat next to the window and did the best I could but on overcast winter days I would come home from school and crash for at least 4 hours wake with pounding heart - palpitations strong enough to audibly shake the sheets on my chest (I guess I had hyperacusis too) often covered in sweat and yes with that strong need to urinate and drink a litre or two of water with such an urgency ... well you know.
Back then I would usually follow the water with some food and then go back to sleep till 7 something the following morning. As long as I could before being forced to repeat the procedure.
I now think that I have had PoTS since I was a teenager. perhaps not severe enough to actually meet definition - I was not tested so neither I nor anyone else can really know - but my consumtion of water was always over the top.
I can remember a family friend being surprised one summer when I downed almost 1.5 litres of water in one go. My memory is of being confused by her surprise. To me this was normal. I would get home from school and have at least 2 x 375ml glasses of water often 3. And I can remember a backpacking holiday where I was buying more water than the two people who were traveling with me (yes combined).
Now that I think about it my memories seem to be filled with such moments, and examples of lightheadedness too of course.
Anyway early on in CFS/ME I spoke with a biochemist who put my then heavy water consumption (I had just done a 24 urine test where I produced something like 14 litres of urine). The biochemist said that this was pretty normal (elevated urine though not to my degree) in people in severe pain.
His explanation was that people in severe pain use up neurotransmitters faster than they can recycle them and that the extra water was needed to wash the breakdown products out of the system. Indeed I seem to remember him talking about this producing pressure of their kidneys.
Which could be part of it (I had severe chronic migraine and CFS -- yay). But PoTS is made worse by inflammation and migraine is inflammation.
Glucose could still be relevant I know that after my most recent case of this - 3 days a go - I had a stronger than usual desire for carbs - I almost ate two weeks worth of fruit in two days and broke my usual pattern of intermittent fasting.
I know that the research team in melbourne has found that pwcfs/me have high/ high normal glucose 1st thing and that someone else reported research that showed low glucose (presumably later in the day). Neil McGregor said something about it in the morning Q&A session at the stanford conference.
So it is possible that ME/CFS blood chemistry is weird and that this weirdness is somehow related to these symptoms.
My only suggestions are salt and potassium chloride, plenty of water and rest and most importantly don't get ME/CFS or PoTS. Unfortunately I have no idea how to achieve the last of these.
Last time I think I also took some multis, extra b2 creatine and alcar and anything else that I though might do some good - but I do not know that they did any good or any good that related to these symptoms.