I try to say away from caffeine nowadys. Once I was up pretty much up all night studying for two midterms the next day and others that week and was getting very little sleep. So in the morning I thought I'd drink a few Cokes/Pepsis to liven up a bit, and boy did I. During the second test that day, think calculus, my hands began to tremble, BP rose, I got the shakes and I really physically lost it for a few minutes. I calmed down after that and still got a 98% on that test - but ever since that experience I have tried to avoid caffeine whenever I could be in stressful situation.