One of the ways that garlic helps you overnight is that is can clear blocked nasal passages. The allicin, when breathed, thins mucus so that it drains. Your breathing will improve, which in turn makes it a lot easier to fall and stay asleep.
If simply placing a clove or two of garlic under your pillow isn’t enough, you can make a garlic steam to breathe before bed. Simply place 3-5 crushed cloves into a pot of boiling water, turn off the heat, and then inhale the steam. Be careful not to get so close to the pot that you burn your face.