To help you understand why you're a monster before your morning coffee, the scientific minds at AsapSCIENCE put together a video explaining coffee's effects on your brain. There's some stuff about receptors, and something called adenosine, but that's not important. Wanna know why coffee hypes you up? It does the same thing to your brain as crack.
Caffeine hypes you up by increasing the production of adrenaline, but it also spikes the dopamine in your brain, which is exactly what cocaine does when it hits your system. Obviously, caffeine does this all to a lesser extent, but coffee is a drug, and so it has a few things in common with the more hardcore stuff. AsapSCIENCE further explains that there is a lethal dose of caffeine, though it's kinda impossible to achieve. To OD on lattes, you'd need to consume 150mg for every kilogram you weigh. We're talking thousands of refills, and your stomach wouldn't physically be able to hold it all. Plus, even if you somehow acquired an elastic stomach, you'd be experiencing fits of mania and hallucinations long before the critical point.