Fainting Spells After Sex

My boyfriend and I don’t have sex often. Maybe like once or twice per month. It’s by choice on both of our ends. Anyway, after we have sex, I get super dizzy and see dark spots. My heart races. I usually struggle to get up. I’ve even fallen to the floor once but didn’t pass out. I was just was wondering if anyone else has experienced this and if anyone had any advice. I don’t think it’s because I’m hungry or dehydrated. I eat and drink a lot. Lol