Someone who's fretful can't relax. You might be fretful — upset and fidgety — if you're waiting to hear whether or not you've been accepted into a competitive summer music program.
You may be fretful because you're worried about a friend, you're waiting for news, you're incredibly irritated with your little brother, or simply because you're an anxious and restless person. The word at the heart of fretful is fret, a verb meaning "worry" which is rooted in the Old English fretan, "to eat or devour." From this, fret grew to mean "being eaten away by worry."