It was just the one time, right? I wouldn't worry unless it is a problem that continues to occur. MrsD made good points about that much time sleeping and becoming dehydrated, which would of course make you dizzy in this situation (just getting out of bed).

If it does happen more often, then you should do some self orthostatic checks (BP's laying down, then sitting, then standing) and see if your systolic BP drops more then 20 points.