Someone who's hyper is overly excited or energetic. If coffee and tea make you feel a little hyper, you might try switching to decaf!
Hyper is a shortened form of hyperactive, a behavior that includes restlessness and sometimes inappropriate amounts of movement. It's part of an official diagnosis, attention deficit hyperactivity disorder, or ADHD. But hyper also describes any excessive activity or feeling or excitability: "I want one of these sleepy kittens, not those hyper ones climbing the curtains." The Greek root of hyper means "too much," and when someone is hyper, they really are too much!