Answer by Johnathan Henry:
Try a "Scottish shower."
Start with a regular hot shower to loosen up and get comfortable. After a couple minutes, turn the temperature to cold. You can do this gradually if you'd like, but I personally just smack the handle towards cold and go on with shower. You will freeze, you will find it difficult to stay in the water, your breathing will become short, but this only lasts about 30 seconds in my experience and is actually very invigorating and exciting.
Let the cold water rush over your face. Doing so activates something called t where your heart beat slows and your blood is redirected to your internal organs. Once you get used to the temperature you'll notice yourself feeling a lot better and a lot calmer. Certainly not sleepy or groggy.
Turn the water back to your favorite temperature and your blood will rush back into your extremities. A "true" Scottish shower alternates the hot and cold several times, greatly increasing your circulation and further energizing you.
This is a very simple way to quickly wake up. A lot of people are very hesitant about turning on the cold water. I find the cold water to be very soothing after the first 30 seconds, and remember, you can always end on hot water!