Lots of us have issues with low potassium. I first became aware of this after reading Freddd's posts about B12 and folate inducing potassium deficiency. Here's one of his posts:
http://forums.phoenixrising.me/index.php?threads/warning-low-potassium-is-dangerous.14410/
Another very good post about potassium, this one by Richvank (former member who unfortunately died suddenly a few years ago):
http://forums.phoenixrising.me/inde...ded-in-methylation-treatmt.18670/#post-291410 Rich talks about the particular problems people with ME/CFS have with maintaining adequate levels of intracellular potassium.
I first learned that I had low potassium issues when I started taking methylfolate (had already been taking MB12 for many years) some 7 years ago. It initially boosted my energy, and then after 2 or 3 days I was hit with severe fatigue. Because I had read Freddd's posts, I was on the alert for symptoms of low potassium, and for me the chief one was this awful fatigue, different than PEM. The interesting part was I had had this particular fatigue before, only I never knew what it was. I started taking potassium, titrated up to 1000 mg over a couple of days, and the fatigue abated. I eventually learned that I had to take extra potassium every day, and since then take 800 - 1000 mg potassium gluconate daily, in divided doses, as well as drinking low sodium V8, which has 900 mg potassium per 8 oz. I found I could not get enough potassium in foods.
My serum potassium levels were always in the normal range, albeit on the low side - 4. something.
Other symptoms of hypokalemia I have had are muscle twitches and spasms in legs and feet. I don't get cardiac symptoms, but many people do - arrhythmia, palpitations and so on.