As long as precautions are taken to protect the sheets, sex while I'm on my period is fine by both me and my Master. However, we keep the BDSM play to a minimum. I'm very emotional during my period, and if he takes the play much beyond light play, it takes very little to reduce me to tears and feelings that I've failed him that overwhelm me. We've found it better to just avoid most of that during the week of my period.