I've found this to be true on trans-oceanic flights, but rarely on trans-continental (USA). I wish it were true on all flights - even if it's not a night fligh

I've found this to be true on trans-oceanic flights, but rarely on trans-continental (USA). I wish it were true on all flights - even if it's not a night flight, it's nice to nod off for a quick 20 min nap sometimes.