Feel lightheaded when I stand up...?

No matter how slowly I stand up, I feel lightheaded. I eat very well... no vitamin deficiencies. I don't think it's postural hypotension because my doctor checked and found no severe drop in blood pressure. I have had problems with fainting in the past, but that is only when i have been standing for a while and my blood pools. My doctor also checked for iron levels and heart arrythmias, and i check out perfectly healthy. So I'm baffled. Does anyone have any insight?

You likely do have postural hypotension. I see patients with this all the time who will check out fine in the doctor's office or the ER. The fact is, it just doesn't happen every single time you stand up or change positions and so when you arrive to be checked for it, by golly it just doesn't happen. The absolute most effective test for this is called a "Tilt Table Test". The test is exactly what it sounds like, and it looks to see if the problem originates in your heart, or with your blood pressure itself. (Vascular resistance, preload, etc.) So talk to your doctor about getting a Tilt Table Test done.

Um...maybe you have a headache?

Unless you have some kind of inner-ear problem (which should be ruled out) it sure sounds like orthostatic hypostension.
Buy yourself an inexpensive automatic blood pressure cuff and check it laying down, immediately after sitting up, and standing...and see for yourself.

you might be dehydrated if you drink a nice amount of water you will be ok

when you're standing or laying for a long time your blood vessels dilate and constrict to keep blood flowing despite your position. so, i would get your vessels and valves (inside the vessels) checked out. your dr can run tests to find out for you.... good luck!

Well, when this was happening to me, my doctor discovered it was hypoglycemia. That's basicaly low blood sugar...the opposite of diabeties. Talk to your doctor about this possiblity. Here's some extra info on the topic...

http://en.wikipedia.org/wiki/Hypoglycemi...

It could be due to low blood pressure. That would be my first guess, but you said your doctor checked for that, and you were fine. Remember though, that blood pressure levels can change on a daily basis. So check it at least once a week.

You might also have an inner ear problem called "Vertigo". That can cause dizziness.

I'm baffled too! I do hope you figure it out, though.

Get a second opinion and drink lots of fluids. God forbid it's a tumor...GO to another doctor...get a full MRI