Oh yes, you are definitely not alone in this! From what I have heard, a big reason for that lying-down-is-fine-but-upright-is-miserable feeling is blood pressure dropping when you change positions, so your body just needs a moment to catch up when you move from lying to sitting or standing. The advice that seems to help most is to transition very slowly, like sitting at the edge of the bed for a minute before you stand, and keeping well hydrated throughout the day since even slight dehydration can make the dizziness worse. My friend who had her third baby last year said her gynae flagged this early and just keeping a small snack and water nearby helped her manage it day to day, though every pregnancy really does behave differently. Third pregnancies especially seem to throw new symptoms at you that you never had before, so it is worth not just writing it off as "normal pregnancy stuff." Do mention it at your next check-up or call your doctor sooner if it feels severe, better to have them rule out anything and give you personalised advice.