Because coffee (and the caffeine it contains) is a stimulant the body produces cortisol when we drink it. Cortisol is a ‘stress’ hormone which prompts us to wake up every morning. It also helps us when we are in the fight or flight mode. When this happens the body reacts by releasing its energy stores which are normally reserved for use when we need to fight to survive. This is why we have a surge of energy which is responsible for giving us the extra strength we need to ensure our survival when we are faced with a dangerous situation. If our store of energy is not replaced, we feel drained when the boost we experienced because of our caffeine intake has dissipated. The caffeine in our coffee will use up our muscle glucose and so our blood sugar level falls. This loss of blood sugar can cause us to feel sad, tired, or irritable.
There are other possible reasons for experiencing tiredness after an intake of caffeine. One of these is that you are stressed or exhausted, or both, so the crash that usually comes after drinking coffee is exacerbated.
Another possible reason is that you suffer from Attention Deficit Hyperactivity Disorder (ADHD). If you do you have probably realized that you react to stimulants the way other people react to depressants.
Another possibility is that you usually drink coffee in particular circumstances and perhaps you drink it with a certain food or even with another drink which makes you feel sleepy. In such a case you notice your reaction to coffee, but it isn’t the actual cause of your tiredness. You will need to stop eating some foods to find out which could be the problem ones. Eliminate all those which could potentially be causing your problem for a month. You should also stop drinking coffee for the same period. Then you can reintroduce coffee into your life slowly. Try drinking your usual amount of coffee for one day only and monitor your reactions. If you don’t react, coffee isn’t your problem.
If coffee isn’t the problem, you may need to monitor your intake of caffeine which is contained in high-energy drinks. In fact, the less you consume them, the better for your body.
Make an appointment to see your doctor an explain how you feel. You might be allergic to a certain food or drink. Tests can be carried out and hopefully the offending foodstuff or drink can be found and you can eliminate it from your diet!