Has anyone ever started their period while having sex??

My boyfriend and i were having really amazing passionate sex last night. I guess we both thought that i was really wet down there. when we finished, he went to go grab me a drink and smoke a cigarette. I went to go pee and I was mortified to realize that i started my period, i went back to the room and sure enough there was blood on the sheets. I started crying because of how embarassed i was. Thankfully my man is extremely understanding, he wasnt even worried about it.