I would caution use of fludrocortisone unless it's absolutely necessary. It's a corticosteriod, and they don't mix well with Lyme disease.
Of course, with that being said, if you are bordering on your adrenals shutting down, then the use of whatever means necessary to get them back on track would be much more important than worrying about
what it will do to a Lyme infection.
Did this start when you started using/doing something? If so stop doing it, whatever it is, until you can talk to your doctor.
I'm so sorry, but I can't remember all of your details!
In this article, a woman had severe hyponatremia (low sodium). Here is what is said in the last paragraph:
"After 5 days of antibiotics and fluid restriction, her serum sodium returned to 130 mmol/L with improvement in her neurologic symptoms. After completion of 21 days of antibiotics, her serum sodium was within normal limits and her neurologic symptoms had almost completely resolved."
www.ncbi.nlm.nih.gov/pmc/articles/PMC1781324/ So maybe you really should stop drinking most of your water, at least until you can get this under control. You need to see a doc that will test you with a 24 hour saliva test to see how much and when your adrenals are producing their hormones, and go from there in my opinion.
And I strongly suggest not using the FIR sauna until this is under control either.