I’ve been asked recently by a friend why she finds herself awakening at 2 a.m. virtually every morning.

Many people have experienced this phenomenon, a tendency to awaken at least briefly around the same time every night. There may be many potential reasons for this, ranging from your pet to a need to urinate or a spouse coming to bed for sleep later than you. The expression of certain hormones in your brain throughout the night might play a role.  However, for many people, these brief awakenings may also be related to your brain’s natural rhythms for sleep.

To describe human sleep physiology as simply as I can, human sleep is very dynamic. We sleep in cycles, called ultradian cycles, in which lighter stages of non-REM (called stage N1 and N2) sleep are followed by deeper forms of non-REM (formerly called stage 3 and stage 4 sleep, but now called stage N3, or slow wave) sleep and then, to varying degrees, rapid eye movement (REM, stage R, or dream) sleep. In general, the amount of deep non-REM sleep we have per cycle is highest during the first one-third of the night’s sleep, and the amount of REM sleep we have per cycle gradually increases as the night progresses (which explains why we tend to remember our dreams most around, say, 4-6 a.m.). Exactly how and why we have been designed neurologically to sleep in this way are a mystery. A typical human adult’s ultradian cycle lasts for about 90-110 minutes. Generally it’s most difficult to awaken fully from N3 sleep, and it’s quite easy to awaken fully from REM sleep. This explains why you often feel very groggy if you’re awakened abruptly during the first 2-3 hours of sleep, but may find yourself awakening easily and quickly from a dream later at night.

The primary point I want to make with all this is that between these ultradian cycles, there are normally and naturally periods of arousal from sleep. There can be several of these brief arousals in a typical night.  In children, adolescents, and young adults, these arousals are generally very brief, perhaps lasting for only several seconds; these awakenings are not usually enough to remember, in part because younger people tend to have a lot of slow wave sleep), leaving you with the feeling that you are sleeping uninterrupted all night long, even though you have likely in reality aroused several times. Once you reach middle age, however, such as your 40’s and 50’s, the tendency to recall these arousals from sleep can gradually increase, and the duration of the typical arousal from sleep may gradually increase as well. This may explain why some people remember awakening, say, at 3:30 a.m. on the dot every night. Finally, when you become elderly, in your 70’s and 80’s, say, still more frequent awakenings may occur due to the naturally increased sleep disruption that occurs as your brain becomes more brittle with age.

Why is this all important? Because some people freak out over a spontaneous recalled arousal from sleep in the middle of the night, and this substantial concern or annoyance can generate enough worry or frustration to actually cause persistent wakefulness subsequent to that arousal, potentially triggering chronic insomnia.

Take-home point here: if there is a brief awakening around the same time most nights, and there is no specific symptom or problem that causes the awakening, and if there aren’t substantial problems falling back to sleep, and if there is minimal sleepiness during the day, my sense is that the awakening is probably not much to worry about. If there are substantial problems associated with the awakenings, however, it may be worthwhile to bring that to a doctor’s attention.

Have a great evening, everybody, and sleep well!