Before I got diagnosed with POTS, my first cardiologist told me that my symptoms were just dehydration. Many people with POTS actually have chronically low blood volume which can feel like dehydration.
When I stand, I feel out of breath and shaky, as if I just completed a workout. My heart beats really quickly and all my body can think about is "when do I get to lie down again?". After a while of feeling this way my body decides to take matters into its own hands and forces me to lie down by fainting.