Melatonin is the sleep-promoting hormone that gets you ready for sleep. It should be at its peak at around 3 AM at night. So if you are waking up at 3 AM, you could be deficient in melatonin (from certain medications for example that can lead to melatonin deficiency).
Cortisol, on the other hand, opposes melatonin and should start to rise closer to waking. It helps you wake up.
Elevated cortisol at night is a common problem that can result from long-term stress. Elevated cortisol will suppress melatonin, making you feel “wired but tired” at bedtime.
I go deeper into these top 3 reasons in the video above, make sure to watch until the end!