Normal endocrine systems peak at around 3 AM and are at their lowest at around 3 PM. If you happen to wake up at 5 AM vs 8 AM, you will feel more energetic. Th

Normal endocrine systems peak at around 3 AM and are at their lowest at around 3 PM. If you happen to wake up at 5 AM vs 8 AM, you will feel more energetic. This is because, historically, our main predators were nocturnal, while we hunted almost exclusively in the two twilights (we have substantially better twilight vision than virtually any animal). So when the wolves came at 3 AM we'd be at our most energetic and when it's relatively safe (3 PM in daylight year round), we'd be taking a ciesta. If your body is off hormonally, grogginess throughout the day is a primary sign. When my body was substantially off from ages 18-24, I actually became completely nocturnal, just because 12-5 AM were the only times I felt anywhere near energetic.