Caffeine is a stimulant. It works on your central nervous system. In simple terms, it triggers the stress response of flight or fight, resulting in symptoms like pounding heart, shallow rapid breathing, dry mouth, sweaty palms. Some people who are more sensitive to caffeine can get quite shaky. I'm not surprised if high amounts of caffeine in your drinks make you feel high strung or even aggressive. A cup of strong coffee would do it in a sensitive individual, but for someone who's a habitual drinker, the effects may not be as noticeable. Of course, it does not mean that it's not doing any damage, just that the damage is going on under your radar.