Oral sex during period???

My boyfriend and I have been together 10 years (15-25) 
We have been having sex during my period for a few years now and we're comfortable with it (okay, we reeeally enjoy it?) but early this morning he took it a step further and went down. Initially, I was grossed out and I asked, " what are you doing?" But once he started I just relaxed and let him go. It felt good and eventually I stopped thinking about it but I'm still in shock and just wondering if anyone else does this. I don't know anyone who has but I'm sure we're not the first.