Swollen breasts after sex?

So my boyfriend and I had sex last night, and afterwards, my breasts seemed swollen and heavy. The top half of my body was off of the bed during, so my breasts were pushed more up toward my chin. I've never had swelling like that afterwards before though. And now they are back to normal so I'm just wondering if it just happened because I was upside down sort of? More blood flow to my chest?