Fight or flight
One of the many reasons people drink coffee is to increase their alertness. This is possible because caffeine blocks the effects of adenosine, which is responsible for making you feel tired. The increased alertness comes from the caffeine triggering adrenaline to be released.
When adrenaline is released, you get increased energy. However, adrenaline is also known to be the fight or flight hormone. When high doses of adrenaline are released in your body, you can get very nervous or anxious.
Caffeine-induced anxiety
In fact, caffeine-induced anxiety disorder is actually a thing. It is just one out of four caffeine-related disorders included in the Diagnostic and Statistical Manual of Mental Disorders (DSM), which was published by the American Psychiatric Association.
According to the DSM, high daily intakes of 1,000 mg or more caffeine each day causes jitteriness and nervousness in most coffee drinkers. Moderate daily doses of coffee can also lead to similar effects for those who are not coffee drinkers. Even modest doses can cause increased stress levels and rapid breathing for caffeine-sensitive individuals.