GD question

If you had GD and knew it before you were tested, what did it feel like? About an hour or so after I eat, I getting really lightheaded/dizzy and feeling like I may pass out. I’ve also been having headaches and black squiggles in my vision during these episodes. I just feel very “out of it” or tired, too. I’ve been checking my BP and it’s been perfect. But I don’t have a glucose monitor at home. I’m 27 weeks, my glucose test is scheduled for next week.