I started drinking a lot of coffee after coming to college. I became instantly energized and social after grabbing a cup or two. But then at night I became extremely dull, unsocial-able, and quite depressed and completely lack of energy and I crashed into the bed just to wake up late in the mornings. Why is this happening?
Because coffee and other stimulants do not supply "energy" - they cause your body to use its energy reserves a greater or prolonged rate than it normally would.
Your body does not burn/feed off the caffeine, the caffeine causes your body to burn glycogen/glucose and fat.
So, naturally, once their effects wear off, and your body returns to it's normal state, the energy stores are going to be more depleted than they usually are, and your body will recognize that as feeling run-down afterwards.
That's to be expected. If you use more energy and engage in more activity, one should feel more tired afterwards.
This effect is known as caffeine withdrawal. It's normal that you may feel a bit loose of you don't have caffeine after a while. The whole set of adverse effects of caffeine withdrawal is enlisted as:
- depressed mood
- difficulty concentrating
according to WebMD.
I think there are two potential issues -
(1) The coffee is masking underlying fatigue, as outlined here:
Since caffeine works as a central nervous stimulant, it will cause the body to “forget” that it is tired. When used in moderation, caffeine can help to keep energy levels up during the day. The caveat is that tolerance is built quickly; to make up for adenosine receptors that have been inhibited by caffeine, the brain will create even more receptors. As a result, more caffeine is needed to keep drowsiness at bay.
When the brain detects increased adenosine, it will make you feel even more tired than if you’d never picked up a cup of coffee at all. Now, you’ll need even more caffeine to keep energy levels up and help your brain to function at its best.
(2) Along the lines of Coffee Withdrawal in an earlier answer, coffee affects neurotransmitters like serotonin. This is a good resource that might explain the issue further: Coffee and hormones: Here's how coffee really affects your health.