You participate in a sleep study at a university clinic. the researchers measure your body chemistry while you are sleeping. which hormone do they find follows a circadian rhythm and peaks just before you wake?

The hormone they would measure is melatonin. In animals, this is a hormone produced by the pineal gland which regulates sleep, but has an anti-oxidant function in plants. Melatonin synchronizes the circadian rhythms of animals including timing of wakening and regulation of blood pressure.