I've found electrolyte drinks to do OK for me. I have no significant hypotension, so re-hydrating doesn't seem as key for me, though I still try to keep up with hydration and electrolytes.
I've often wondered if a Medic Alert bracelet would be warranted for people with OI. I've never passed out from OI, but I suppose it could happen in a public place (or I could at least get woozy enough to be non-responsive). Would EMTs even know what "POTS" means or what to do about it? I have no other obvious reasons to need a bracelet, like medication allergies.
I've got a few POTS friends (POTS only, not ME/CFS) as well as ones with NMH and other forms of dysautonomia, and this topic has come up a few times. Its tricky to put POTS or dysautonomia on your medi alert bracelet if the docs/ambos have no idea what it is. A medi-alert bracelet is probably a good idea if you are prone to passing out (especially in public).
Asking your doc might be a good idea about what to put on the bracelet. Some suggestions could include: tachycardia, postural syncope, low blood pressure, seizures, fainting, tremors (if you get bad shakes), cardiac, autonomic dysfunction, labile BP & HR. You could also put check wallet and have a card with more info about your meds, conditions and specialists.
I dont have one myself as I'm not usually a fainter with my POTS, unless I'm really dehydrated & sick.