characteristic of NREM dreams, potentially disproving that theory. Research has also shown that dreams during the NREM stage most commonly occur during the morning hours which is also the time period with the highest occurrence of REM sleep. This was found through a study involving subjects taking naps over specific intervals of time and being forcefully awakened, their sleep was separated into naps including only REM sleep and only NREM sleep using polysomnography. This implies that the polysomnographic occurrence of REM sleep is not required for dreaming. Rather, the actual mechanisms that create REM sleep cause changes to one's sleep experience. Through these changes, by morning, a sub-cortical activation occurs during NREM that is comparable to the type that occurs during REM. It is this sub-cortical activation that results in dreaming during the NREM stage during the morning hours. Self in dreaming It is suggested that dreaming involves two selfs: aggressive self (REM) and friendly self (NREM). It seems that in NREM dreams, the self are put in different situations, largely negative, but are found to respond in a way that befriends or embraces the unfamiliar. It's sometimes thought that in NREM sleep, the dreamers are "aware of being aware", also known as "secondary awareness", which allows them to make better decisions and be able to reflect on them. Muscle movements During non-REM sleep, the tonic drive to most respiratory muscles of the upper airway is inhibited. This has two consequences: The upper airway becomes more floppy. The rhythmic innervation results in weaker muscle contractions because the intracellular calcium levels are lowered, as the removal of tonic innervation hyperpolarizes motoneurons, and consequently, muscle cells. However, because the diaphragm is largely driven by the autonomous system, it is relatively spared of non-REM inhibition. As such, the suction pressures it generates stay the same. This narrows the upper airway during sleep, increasing resistance and making airflow through the upper airway turbulent and noisy. For example, one way to determine whether a person is sleeping is to listen to their breathing - once the person falls asleep, their breathing becomes noticeably louder. Not surprisingly, the increased tendency of the upper airway to collapse during breathing in sleep can lead to snoring, a vibration of the tissues in the upper airway. This problem is exacerbated in overweight people when sleeping on the back, as extra fat tissue may weigh down on the airway, closing