Why don't we feel hungry after waking up?

Question

Yesterday, I was fasting (drinking only water until I had dinner at 9 pm). After dinner, I went back to my lab (I am a Master's student) and worked till 1:30 AM. By 1 o' clock, I was feeling *quite hungry*, probably because I hadn't eaten anything all day and only had a light meal for dinner. However, I didn't eat anything then and just slept. Today morning I wake up (around 9 AM) and I don't feel hungry! I could surely eat something if I wanted, but I am not feeling the acute hunger that I was feeling last night!**More generally**, what could be the reason for the behavior that a human experiences acute hunger, but after sleeping for an extended period of time, he/she may no longer have the hunger. Since a passage of time has passed, one would expect the hunger to increase, which would have certainly happened if the person had not slept. Is it the case that sleeping somehow affects the overall hunger/glucose demands of the body? I suspect that it is possible that the body's food needs could be majorly affected by the circadian clock, but I wanted an explanation to contrast the situation when one is *not hungry* and when one is *very hungry* before sleep. How can the difference between both the situations be easily trumped by the circadian rhythm's effect? (*if it is the explanation!*)

Answer 1

True hunger occurs when the stomach contracts. The stomach contracts its been empty for a while. You said that you were fasting. I take this to mean that your stomach had been empty for a while and had contracted several times during your fast. When you went to bed, your stomach was contracting, so you felt hungry. When you woke up, your stomach was at rest, neither expanding nor contracting.