@GlassCannonLife - it's been difficult for me to find a good phosphorous supplement. Here's a post I did about phosphorous recently where I explain what I'm taking - it's sort of complicated:
what’s the rundown on high dose thiamine? | Page 4 | Phoenix Rising ME/CFS Forums
Also, one more post with a bit more info:
what’s the rundown on high dose thiamine? | Page 4 | Phoenix Rising ME/CFS Forums
If you read the posts and look at the links, you'll see that the product I'm currently taking
Sodium, Potassium, Phosphorus Powder Concentrate (Sugar Free) 100 Pack – Hargraves Online Healthcare (hargravesotc.com)
has 250 mg of phosphorous per packet, which is 20% of the RDA. My need varies from 1 to 3 packets a day. I determine this by muscle testing. Also, symptoms give me a clue - when pills start sticking in my throat or I get double vision, it indicates I'm getting low - it affects the small muscles first. I don't recommend that anyone try to use muscle testing to figure out what they need unless they are very familiar with MT and used to figuring things out for themself and also go slowly and carefully. Unfortunately, the company I buy this from is currently out of stock - I hope they get more because it's the best product I've been able to find.
I have also had good results working with a chiropractor doing muscle testing in determining if I need a particular thing and also how much.
And of course one would hope your doctor could help with this.
I just found this which appears to be an equivalent product - unfortunately, it costs more than twice as much!
Amazon.com: MCK27102700 - Cypress Pharmaceutical Phos-NaK Dietary Supplement Sodium / Potassium / Phosphorus 160 mg - 280 mg - 250 mg Unit Dose, Oral Powder Concentrate Packet Fruit Flavor : Health & Household
I just found another source (I've never ordered from this company:
Phos-Nak, PDR 278-164-250Mg 100ct. - The Online Drugstore © which is cheaper than on Amazon, though pricier than the Hargraves product, which is out of stock:
Sodium, Potassium, Phosphorus Powder Concentrate (Sugar Free) 100 Pack – Hargraves Online Healthcare (hargravesotc.com)
If you try one of these, I can't tell you how much to take. I just experimented and used my muscle testing.
I did get a prescription from my doctor for Phos-Nak, but I had trouble getting enough pills from her, she wouldn't understand how my need changes daily, and also it didn't seem as effective as the little packets. Though if I had enough of it, it would probably work fine.
Foodwise - dairy is high in phosphorous, you can do research on the best foods.
Did your doctor or anyone give you phosphorous after your blood test? I've experienced low phosphorous and it made me VERY tired, as did low potassium. So it's possible that your very bad crash was actually a symptom of low phosphorous, possibly combined with low potassium. That could be very rough.
Did anyone recommend potassium for you as well?
If you can tolerate dairy, you might try drinking several glasses of Kefir (that's what I did when I suspected low phosphorous after starting thiamine) - doing this caused my energy to start to return within a few hours. I was so relieved!
And I've found that drinking 2 or 3 or 3 even 4 glasses of low sodium V-8 (or equivalent) can help restore potassium levels within a few hours as well.
Do doing both these things might give you an idea of what's going on, if they make you feel better. And then you can decide how to proceed.
Also, I can't remember what I've written where, but it is possible to have low
intracellular levels of potassium even if one's
serum levels (your blood work) are normal or low normal. See
Why is potassium supplementation needed in methylation treatmt? | Phoenix Rising ME/CFS Forums
My potassium levels were always low normal, but I've been hit by low potassium several times and it would leave me wiped out for days, until I discovered what it was.
Ideally you'd be able to talk to your doctor about all this, but unfortunately most of us don't have ideal doctors.