What Causes Dizziness And Fainting Spell After Having Sexual Intercourse?

Hi, My girlfirend and I had sex at around 2:30 today, and afterward she said she felt light-headed, then she started to faint. I then carried her upstairs and put her on the couch and gave her some water hand put a cold compress on her head as her forehead was starting to increase in heat. About thirty minutes later I let her get up again slowly because she had to make it to an appointment, but when she got home around 6:30 she fainted again, this time falling and hitting her head. I'm very worried and will answer any questionif it means I can find out what happened and how I can help her