Say you are an over 40yo guy who preferred to have sex in middle of the night or morning rather than at bedtime because... well... because those are usually your body's best times to have sex. What would cause a surge in your energy level where all of a sudden you would be able to enjoy bedtime sex as well?
I only ask because this is what we are seeing in our marriage bed. GR, who is in his late 50's, would sometimes be too tired at bedtime for sex so he would sleep 3-4 hours and then wake me up for sex, which was fine for me. More and more he has been enjoying sex even at bedtime. The other day I briefly asked about it and he said that he knows I sleep better after sex. (My man can sleep anytime when he is tired.)
As you can see, I am a curious soul. I always want to know the reasons why things work the way they do.