I’ve found the opposite. If I fast for more than 24 hours, I struggle tremendously with sleep. I imagine it’s because my sympathetic system is somewhat in overdrive vs normal eating days, keeping me wired.
I do tend to always sleep better if I eat a small amount of carbohydrates before bed, too. I always figured it was because my body was in ‘rest and digest’ (parasympathetic actions of digestion kicking in). If I eat too much, however, then yeah… I struggle to sleep.
I don’t think digestion during sleep is slowed down significantly (at least I’ve not come across this), but lying down very soon after eating could increase the likelihood of acid reflux.