I have this problem horribly...more than likely its whats called orthostatic hypovolemia, which is just fancy for "head rush". Theoretically what happens when you are sitting is your body works harder to pump blood to your legs and so your vessels dilate. Then when you stand uo, blood rushes down to fill the vessels, unfortunately draining it from your head. Staying well hydrated a "dangling" as its called before standing up should help a lot. Sit on the side of bed or couch and try to lean back just a little for about a minute and get up slowly. It prob wont stop completely, but should keep you from going down. If the dizziness is constant however and doesnt go away it is prob something diff and possibly related to your bp so if thats the case nake sure to contact your ob.
Sorry so long winded!
