You can still have postural hypotension and combined with dehydration the fainting spells can be worse. The issue mainly is being on your feet all day therefore blood pooling at your feet causing drops in blood pressure.

I'm a nurse too and couldn't understand why when I'm standing I have fainting episodes- my blood pressure was 76/50! Turns out I was iron deficient and postural drops exacerbates the whole situation.

I now drink atleast 2 litres at work and put my feet up on my breaks (when I get them ) lol