The primary cause of chronic difficulty staying asleep near morning is insomnia, which is defined as difficulty falling or staying asleep and is frequently associated with early morning awakenings. These awakenings may occur throughout the night, but they tend to be more frequent in the second half of the night, due to a diminishing ability to sleep toward the morning hours.
The ability to sleep is linked to two processes, one called the homeostatic sleep drive and the other being the circadian rhythm (which will be discussed later). The homeostatic sleep drive is the gradual desire for sleep that builds the longer a person stays awake, and relates to the gradual accumulation of a chemical in the brain called adenosine. This “sleepiness signal” eventually helps to initiate sleep; during sleep, it is cleared away so that midway through the night, the desire for sleep is depleted.
By morning, it should be nearly gone.
If a person awakes during the night—and especially if this awakening occurs toward morning—the ability to return to sleep will be compromised due to the lower levels of adenosine. Sleep may be greatly delayed, fragmented, or disrupted in insomnia, but awakenings near morning can be especially troublesome.
Anxiety and Depression
Any of the mood disorders, most notably anxiety and depression, can be associated with early morning awakenings, which typically occur in the several hours before the intended awakening. For example, if the alarm is set for 6 a.m., someone with depression may start waking at 4 a.m. for no good reason. How can this be addressed?
As with insomnia, it is important to treat the underlying contributing factors that lead to these awakenings. And in the setting of psychiatric distress, these problems can persist, so it is necessary to treat any coexisting depression or anxiety. This may require the use of medications or counseling with assistance from a psychologist or psychiatrist; in fact, studies have shown that both used in combination are most effective. Insomnia is especially well-treated with cognitive behavioral therapy for insomnia (CBTI).
It is clear that sleep can undermine mood, and conversely, mood problems can greatly affect sleep. By working on both issues together, the complex relationship can be unraveled.
It may seem peculiar to imagine that a breathing disorder such as obstructive sleep apnea may contribute to early morning awakenings. To better understand this relationship, it is necessary to carefully consider the structure of sleep.
It is artificial (but useful) to divide the night in half when considering the stages of sleep. In the first half of the night, slow-wave sleep occurs more frequently, especially among young people. In the second half, rapid eye movement (REM) sleep makes a more frequent appearance. Though the cycles of sleep occur regularly through the night, REM sleep becomes more prolonged towards morning. Therefore, we are more likely to awaken from it near morning and recall the vivid dreams associated with the state.
Sleep apnea has many causes and is also more likely to occur during REM sleep. The muscles of the body are actively paralyzed during this stage, so we are unable to act out our dreams.
(If this does not occur, a condition called REM behavior disorder may result.) Muscles lining the upper airway are also paralyzed, which makes the throat more collapsible—and collapse manifests as disrupted breathing and sleep apnea. Sleep apnea is often worsened during REM for this reason.
Morning awakenings may, therefore, occur in the setting of sleep apnea that is worsened during the periods of REM that become more frequent and prolonged towards morning.