I get this, also.

I just had the gamut of blood work, at my last GP annual physical. I was thinking, BP or Anemia or anything else, under the sun.

Could either be dehydration or side effects to meds or MS, if you ask me. My GP said, could be my MS. So, perhaps, it could just be MS? Could be a fluke, don't know. Just know, that wow...here we all are, on this thread, posting that we have similar experiences.