I have both POTS and a CSF leak. The CSF leak made POTS much worse. I can distinguish between the two because my heart rate only goes way up when I stand but is pretty much OK when I sit. When I sit I got a progressively worse headache. The limited sitting time was the csf leak. The feeling icky and faint when I stand is POTS. I had the leak surgically repaired. POTS improved substantially but it is still there. My doctor (Dr. Schievink at Cedars Sinai) says many small leaks do not show up on imaging, but a positional headache that comes on slowly over time is likely a leak. A headache that you get whenever you stand up is more likely POTS.