Hello. My doctor suggested I might have orthostatic intolerance because when I stand up from either a sitting position (riding in the car) or sometimes when in a reclining position, my legs become extremely weak (like they might even give out) for a minute or two and then I'm fine. No pain, just weakness. Sometimes I'll hear my heartbeat whooshing in my head at the same time. This does not happen every time. BUT - I also have problems in my spine both lumbar and cervical and need to get new x-rays and an MRI. So I was wondering how OI affects other people. Must one have a big blood pressure change or rapid heartbeat in order to confirm it? Thanks in advance.