Every ninety minutes of every night we’re asleep, a dream unfolds. The short at the beginning of the night are usually no more exciting that the idle thoughts that randomly pop into our heads when we’re awake. But as the night progresses, the length of each dream increases (the last dream can be up to twenty minutes long), the body responds more intensely (increased heartbeat, respiration, muscle twitching), and the become deeper. are sometimes said to be ordinary sequences of images that are experienced by the mind during sleep. For ....