tl;dr—Compared to waking life, dreams are pretty wild and emotionally intense. Example—in a dream last week all my teeth fell out which was pretty distressing, and nothing as interesting happened to me in waking life. How emotional/ extreme an experience is seems like a good proxy for how good or bad it is. So probably the best and worse experiences you’ve had last week were whilst you were dreaming.
And also gwern’s comment:
My own observation is that while my dreams are not infrequently quite unpleasant and nightmarish in content, a corresponding emotional reaction is not there. Many dreams ought to have one waking up in a cold sweat, heart pounding, unable to focus for the rest of the day. (Why aren’t all bad dreams “night terrors”? Why does it decrease with age, and correlate with psychiatric problems?) But even if one were to write them down (and I did for a while in a dream journal) to block forgetting, I feel back to normal practically upon waking, and definitely within a short time.
Compare to “The best and worst experiences you had last week probably happened when you were dreaming.”
And also gwern’s comment: