Today the sense is quite mild: if we feel distracted our minds are not focusing well on some issue. At the end of the 16th century, when the word came into English, both as a verb and adjective, it had a much stronger meaning. Shakespeare himself is the first recorded user of a sense of great mental disturbance, "perplexed, confused", even to the point of madness.
Hamlet, having just met his father's ghost, refers to his head going round and round as a "distracted globe" (Hamlet, I.v.97). This is the usual Shakespearian meaning, applied to people. Just occasionally, there is an even stronger nuance when the word is applied to things: when the King of France says "to the brightest beams Distracted clouds give way" (All's Well That Ends Well, V.iii.35), he means they have been divided or torn apart - a sense that stayed in the language for only half a century.
David Crystal is author, with Ben Crystal, of Shakespeare's Words, published by Penguin