My rabbit left a spot of blood on the carpet

I was petting my bunny like I always do down on our carpet at night. When she hopped away there was spot of blood under where she was laying. She’s acting normal and I can’t find on her where the blood was coming from. Obviously I’m going to call the vet the first thing in the morning as they’re not open now. But has anyone experienced this or tell me what’s going on. She hasn’t left blood anywhere else.