Resting before the big event

I’m 39 weeks with second and stay at home with my 3 yr old. He goes to preschool half day three times a week and I find myself just laying down until I pick him up. Usually I’m doing things all morning and getting ready for the baby but I have no desire. My body is just telling me to rest. I feel guilty and bad for just laying around but for some reason my body is telling me I need to before the big day. Anyone else just super tired? I remember being double tired with my first because I worked a full time job.