One of the most common complaints that I get from patients is that they keep waking up at the same time in the middle of the night and are unable to get back to sleep, or they keep waking up every 90 to 120 minutes. This phenomenon is called sleep maintenance insomnia, when you are unable to stay asleep during the night. In contrast, sleep onset insomnia is when you’re unable to fall asleep in the beginning of the night.
A low-dose version of zolpidem (Ambien) was recently FDA approved as Intermezzo to treat these middle of the night awakenings. It’s purpose is similar to zaleplon (Sonata), which is a very short-acting sleep aid, so it can be used in the middle of the night to get back to sleep, without the “hangover” effects that people feel with typical sleep aids.
There are a number of different explanations for why some people keep waking up in the middle of the night. One theory is that people with insomnia are hyperarousable, with higher levels of brain activity and stress hormones. If it’s due to these factors, why is it that insomniacs keep waking up at the same time? One possible explanation is that it has to do with sleep stages. Humans go through 4-5 cycles of sleep, where deep sleep (slow wave) predominates in the first half of the night and REM sleep is more common in the second half. As the night progresses, the periods of REM sleep become longer and longer. Since we know that throat muscles are most relaxed during REM sleep, you’re more likely to have breathing pauses during REM, especially if you’re anatomically predisposed (narrowed upper airway anatomy).
This can explain why many people say that they keep waking up at 3AM, like clockwork. Some people wake up when REM length reaches a critical period, whereas other keep waking up with each successive REM period. Transitions into and out of REM can also predispose one to upper airway instability.
One thing I’ve noticed is that in almost all cases, severe insomniacs have very narrowed upper air passageways. On endoscopy, the space behind the tongue is very narrow, and most people can’t (or prefer not to) sleep on their backs, since the tongue is more likely to fall back then supine. Dr. Barry Krakow did a study a while back showing that the vast majority of insomniacs who were resistant to sleeping pills had sleep-breathing problems.
What I’m describing is not necessarily obstructive sleep apnea. Once you obstruct or have partial obstruction, you can either continue the breathing pause for 10 to 40 seconds (this is called an apnea or hypopnea). But if you wake up quickly within a few seconds, then it’s called an arousal. Insomniacs typically have lots of arousals.
This is why even if you have classic insomnia, you need to look for and treat any underlying sleep-breathing problems, regardless of whether or not you have apneas.
If you are an insomniac, what time do you wake up in the middle of the night?