idk if this is normal

my friends say theyve never had this happen to them so it surely is confusing. every time i stay in a position for 20+ minutes then suddenly move and stretch, i pass out. its not for a long time, but its always that my vision goes blurry quickly even if i stop stretching. i dont know why this happens. i thought it might be blood flow but it happens when im sitting, standing and laying down. the same thing happened yesterday, i was sitting on the kitchen floor on my phone for around 30 minutes and when i stood up and stretched, i instantly fell. my head hit the corner of the countertop as well as my nose, i fell straight to the ground head first and my hand straight up landed inside the trash can. i did wake up at some point but i couldnt move or open my eyes for a good 20 minutes. and when i did i couldnt remember anything that happened an hour before. when i did i realized i had been pass out for an hour. this isnt the first time and for sure not the last. idk what it is.
also, for what its worth, ive been going out more lately. i dont have many friends, including the ones abroad, but im making it work, i think.