oh my God I just had one right now while I was sleeping and I thought I was literally dying I’ve never experienced anything so real and so intense in my entire life I’m basically so scared to go back to sleep and not wake up I couldn’t breathe
I am no expert and not a doctor but it sounds to me like you are hyperventilating, not breathing properly, when you are asleep your breathing and oxygen levels have to put themselves back to normal, so this could be why or it could be just adrenaline overload from during the day. the lightheadness and the vision being a bit weird would also fit in with the hyperventilating, not breathing properly. I would suggest you speak to your doctor and then you can be reassured that it is not anything medical, that is the first thing to do, as if it is anxiety then at least you know what you are dealing with. Hope this helps. take care. Sam