Only four hours sleep -- stayed awake preparing Sunday School lesson

I only had 4 hours sleep Saturday night with a 1/2 hour nap on Sunday. I taught a Sunday School lesson on Sunday, and I woke up in the middle of the night thinking about the class. While lying awake, I thought through the lesson, and after an hour I knew how I should teach the class. I got up, made teaching notes, got ready, and left for church. I had 7 1/2 hours sleep last night. As a result of this lack of sleep, my waking HR this morning was 51. My body feels tired this morning.