The question in the title: Dizziness on standing and the electrolyte explanation — does this still hold? I will give what I have already checked below so nobody repeats it.
Trying to work out what would count as evidence on Dizziness on standing, before collecting any. This is the part I usually skip and it is the part that makes the rest useful.
If two explanations predict the same observation, observing it does not help. So: what observation would separate them?