What could be the consequences of drinking too much caffeine?

I drank too much coffee and instead of getting the jitters like i usually do, i got like a buzz and i feel really light headed and my heart feels like its beating kind of fast, and its a tiny bit harder to focus my eyes. Anyway I'm not incredibly alarmed but i would like to know if anything serious could possibly happen. I drank about 3-4 cups of espresso (espresso made in a regular coffee machine so not as concentrated), and I'm 5 9' and weight about 130 lbs, and have a moderate caffeine tolerance.