from what you wrote it sounds like you might have orthostatichypotension. this long word just means a too low blood pressure when you change positions, like from sitting to standing. it is quite common. it happens when the heart does not have enough time to adjust to changes in position resulting in low blood flow to the brain which may cause you to get light headed, dizzy, or pass out. just be careful to stand up slowly, don't just jump up and go.
it happens to me occasionally when i sit on the couch for a while and then i jump up and do something, i basically fall into a wall because i get realllly close to passing out, and it has happened to other people i know as well, i dont kno what its called but im just telling you this so you can rest assured that you are normal, just take things slow and if you know youre gonna pass out just sit down again.
an additional note is that i can almost guarantee it is related you your heart and blood flow/pressure going through a big jump because the elderly actually have heart attacks in the morning more often than ever because when they get up too quickly their heart cant handle the change in blood flow/pressure and such
soo yea :]
Sounds like something my mother had...it was a variant of Vertigo apparently.