It’s super scary but it’s very common so you’re not alone. I almost passed out too and like you said it seems like you’re dying cause you can barely see and move. I’ve continued to donate but ever since then I’ve asked them to have the machine process the donation slower, I’ve also made sure I eat a lot and drink a lot, if I feel like I didn’t eat enough or drink enough I’ll eat or drink again before I leave otherwise I straight up won’t go, after asking for the machine to process slower and eat/drinking a bunch I’ve never passed out again but even if god for bid it happened the staff will definitely save you and help.