Sudden Dizziness While Lying Down

I have POTS (Postural Orthostatic Tachycardia Syndrome), which does this when I change positions. I also think there is something else going on, as I have chronic hypoxia and hypoxemia with no (yet) known cause, but I'm guessing it is my lupus.

This happens to me all the time. No clue what it is but you're not alone

I have a fainting disorder and low blood pressure. That literally just happened to me today. I was sitting and was very dizzy. However, I don't really know why it actually happens. I know this doesn't help, but you're not alone. Lol. It happens.