Caffeine lifts your mood and helps concentration for those with a poor attention span. It can be a good thing, so long as you don't overdo it. That's the trick, really--the line between a beneficial amount, and increased anxiety/jitters, is pretty blurry.
Caffeine
I'm really sensitive to caffeine and if I'm already feeling anxious, it just helps launch me into panic mode. I don't really like the jittery feeling either. I've cut out pretty much all caffeine except for the trace amounts in green tea (and I'll treat myself to coffee drink on the weekends). I find I'm sleeping much better too since I reduced my caffeine intake.