Sleeping is actually time travel. What you think are dreams are really fragment memories of your adventures in another time. However, to protect yourself and the fabric of reality from utter destruction, you wipe your memories before returning to your time, a few hours after you "fell asleep."
You may find yourself wondering, "But what about the fact that I can see other people when they sleep. They're obviously there, so they can't be time traveling." Pay no attention to that. Your mind is playing tricks on you. You've never actually seen another person sleeping.