We have proposed two theories that may explain why anxious insomnia patients might develop sleep breathing problems.
First, an enormous number of patients with mental disorders suffer from unwanted bouts of sleeplessness that plague them for years. As it turns out, insomnia itself seems to increase your risk for sleep breathing difficulties, because insomnia causes you to spend too much time in lighter stages of sleep. In these lighter stages, your breathing is more susceptible to disruption from abnormal breathing events. Thus, while the mental health patient might start out with insomnia and no sleep-disordered breathing (SDB), it's possible SDB can develop over a period of persistently fragmented sleep.
We also speculate that emotional distress, particularly anxiety, directly impacts the human airway, causing some type of tension or restriction. In other words, we wonder whether a person can develop SDB just by being nervous for so long that it adversely influences breathing.
Eventually, changes caused by insomnia and emotional distress may foster the clinical emergence of sleep-disordered breathing, particularly in a less apparent form known as upper airway resistance syndrome (UARS). We have worked with many trauma survivors who reported no sleep problems prior to a traumatic event. Then post-trauma, they developed anxiety, nightmares and insomnia, which were never fully treated. As their sleep got progressively worse, they were eventually tested and found to have SDB. It would be very interesting to find out how early in the course of their sleep problems they actually developed the first signs of SDB. For these reasons, we are now much more aggressive in recommending sleep testing for insomnia as early as possible.