I could tell only because he'd been head down for awhile but all of a sudden I could eat a lot more without feeling like id explode!
You might just be feeling a difference because the baby changed position. Changing to head down s/he sits lower without having technically dropped.
Oh and when the baby drops, people start greeting you with "woah, you poor thing, you haven't had that baby yet?" Seems even the layperson can sense you're about to go.