I'm not sure of normal but I know I had a few 80/60 days early on in this pregnancy & during labour it got to 80/50 when they started getting nervous...

I was pretty dizzy throughout pregnancy when my BP was low & I made a conscious effort to drink heaps of fluids to keep up my BP. I would drink around 2.5 litres daily... and that was all clear fluids & juices. Not counting things like coffees or teas which can dehydrate you as well. HTH!