Many people wake up suddenly at 2, 3, or 4 in the morning. Sometimes this can happen continuously for many days or weeks. Then it can be difficult to fall asleep again.But waking up at the same time every night does not necessarily mean you have a sleep disorder.What happens in our body when we sleep?Our body has a biological clock. It regulates when to sleep and when to wake up.Night sleep is not in a single state. We typically complete three to six sleep cycles throughout the night. One cycle lasts about 60 to 120 minutes.Sleep has three main...