I have a questionable diagnosis of OI (acc. the poor man's tilt test, confirmed by my GP I have it; according to a cardiologist I was sent to who insisted on a 10-min test only, I haven't). However, I was prescribed melatonin two days ago to help me sleep and I'm having what seem to me to be florid OI symptoms that I've not had before; feeling slightly light-headed on standing and within minutes of being on my feet, finding that I'm stooping over and urgently feeling the need to lie down. I've spent most of the last two days lying down because even sitting with my feet up is too much. I've found several links suggesting that melatonin would make OI worse, e.g. this in the Journal of Physiology and this on the Dysautonomia Information Network. Just wanted to alert others to this. I'm finding this side-effect too much to tolerate.