We all like to get our morning jolt from our coffee and studies now show that caffeine does not work like other stimulants. Caffeine affects other parts of the brain when it we face threatening stimuli.
What does this mean? Well, it means that caffeine may affect our ability to perceive what may actually be happening in our immediate environment because it creates anxiety and fear.
Take a look at the actual study and you will see what I mean: http://blogs.scientificamerican.com/scicurious-brain/2012/07/23/is-that-guy-threatening-you-or-is-it-that-extra-cup-of-coffee/