Lack of sleep pretty much affects every system in the body. Metabolism being no exception. Mathew Walker covers this in detail in Why we sleep.
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)
Did you drink water during that time?
Sure a number of your systems are shut down while sleeping that otherwise are active as you are awake, and other become more active.
Just one example is the spike of human growth hormone (typically around 75% of HGH is released during sleep), HGH is directly related to metabolism and weight loss/gain. Also as You probably know actual fat loss (as opposed to water weight) is a function of breathing, as in fat isn't "burned" or you don't sweat out fat, but fat is metabolized a literally breathed out of the body, and during REM sleep breathing is increased.
By no means is this an exhaustive list, but beyond maybe sweating a little more than normal (again water weight not fat loss) while sleeping, any actual weight loss is all a function of hormones/metabolism.
I've seen myself lose up to 5lbs before and after a workout.