Thanks for all your comments.
I haven't had my thyroid tested but when my potassium levels are OK, I don't get tired, so that has been ruled out.
Catriona, sorry to hear about your hubby, my appraisal has been delayed for a few days as there was a major panic at work, someone managed to book 4 events on the same day in the same venue so there was lots of rejigging to be done & lots of emails to send.
Jill, thanks for your suggestion, my kidney function test was fine.
Sarah, I was on a potassium drip last year & the on the ghastly tables for a couple of weeks afterwards. My potassium went back up & has now dropped again. I will check out the recipes on your blog.
Thank you Anon for the tea & soup recipes.
Hilary, I am on BP tablet, but the potassium deficiency predates these tablets by about a year so they aren't likely to be the cause.