Why do I get dizzy when I sit down? I'm fine when standing, laying down, and driving. But at the computer especially, I feel as I'm about to pass out

BPPV? It sounds like BPPV. This is caused by small stones in the inner ear moving from utricle to semicircular canals where they are not suppose to be . They send false signals to the brain and make you feel dizzy. This can be treatable. See an ent doctor. If you have more questions contact me on my Virtual Practice at www.healthtap.com/dryetimyan.