Manic means frenzied. If you drink 18 cups of coffee in a single sitting and haven't slept for three days, chances are you're manic.
If manic sounds like maniac to you, you're on the right track. Someone who is in a manic state is affected by mania. If you're manic you're in a wound-up, fast-acting, unhinged wild state. People with bi-polar disorder experience manic highs and terrible lows. Other things can be manic, too, like the pace of city life or the flabmoyant outfit you're wearing with seven different colors and eight different patterns.