I tracked weight loss for a month. Eating only one meal a day. I recorded multiple times a day my weight. Only in the morning did I actually record any "loss".
So, I did some tests for this. I stayed up all night to see if I lost weight in the morning like every other day, but I didn't.
I slept, woke up in the afternoon, and I had lost .5 pounds from the previous day.
Something special happens during sleep that is unrelated to a general concept of metabolism, but instead a specific process. It's like some kind of processing the bodies does that is related to weight loss/waste management that does not occur at all (or maybe only a little?) when you are awake. (my amateur assessment)