Hello. This doesn't sound like it fits the description of OI but I was hoping someone might shed some light on this before I see a new doctor. For several years I've experienced extreme weakness-jelly legs that begin a few seconds after standing from a sitting position. This never happens when I've been lying down. It happens more often when I get out of the car than when sitting upright at home or a restaurant - though it does happen there too. I never feel lightheaded or dizzy, but I do occasionally also have a pulsating whoosing in my ears when this happens. My legs feel like jelly to the point that I wonder if they'll give out. It only lasts 1-2 minutes and then I'm fine but it makes walking from the car to the store entry bothersome. I have lower back problems and wonder if this could be caused from that or maybe from a circulation problem. Any thoughts would be appreciated. Thanks!