You probably have a very erotic mind and I mean that in a great way because it's an attribute. Many people are distracted by kids, family, social pressures, work, school, finances, etc. and all of those things crush any feelings of eroticism. For my wife, I know that when she reads erotic books or stories, watches porn, or views online dudes (r/dadbod) then it stimulates her mentally and our sex life benefits. I suspect that if you engaged in some erotic (but non-sexual) activities before bed then it might trigger those feelings more while you sleep. At least that is my guess and I would appreciate you reporting back and sharing with us all. You might also be more susceptible while you are ovulating so there may be a physiological cause as well.