Why do you suddenly get chills while sleeping?

Hello, this is Choi Yeon-seung, a doctor of Korean medicine at Baengnokdam Korean Medicine Clinic.

I wake up suddenly feeling a chill at night. Why does this happen? Those who have experienced waking up suddenly to a rush of cold will know what I mean. Suddenly, you feel shivery and cold, your body tenses up, your lips might tremble, or your teeth might chatter.

What's most perplexing is when this happens regardless of the indoor temperature. Even with the air conditioner off and windows closed, you feel a cold sensation rising from within. Even after pulling the covers tightly around you again, it takes several minutes, sometimes over ten, for your body to slowly warm up.

Patients describe this as "It's not just feeling cold; it feels like my body temperature is draining from within," or "I feel a sudden chill as my strength drains away."

As these symptoms recur, sleep becomes more tiring, and the quality of sleep deteriorates. This isn't merely a sensation of coldness. It's highly likely a phenomenon where the body loses its ability to maintain temperature, specifically, the breakdown of its core body heat regulation. Underlying this is a complex interplay of physiological rhythms, exacerbated fatigue, emotions, and digestive function.

Why do these chills occur specifically in the early morning?

Interestingly, these chills concentrate between midnight and the early morning, rather than in the evening or midday. This isn't simply because it's dark and quiet; it's because this period is when our body's circadian rhythm naturally lowers body temperature.

Between midnight and 2-4 AM, the body begins to regulate itself by lowering its core body temperature to maintain deep sleep. This allows the brain and organs to recover efficiently and cool down from the heat generated by daytime activities.

However, if problems arise during this process, the body temperature that should naturally decrease might drop excessively, or the thermoregulation mechanism might be left in a weakened state. Especially when there has been significant physical exertion, or when *sog-yeol* (internal heat) and *geot-han* (external cold, implying a constitution where the outside is cold but the inside is hot) are complexly intertwined, this thermoregulation failure can manifest as severe chills.

Why doesn't the feeling of coldness disappear even when sleeping under covers?

This is one of the points that patients find most frustrating. Often, despite sleeping under a thick blanket, the body feels cold, and there's a persistent chilling sensation from within. At such times, people wonder, "My body temperature isn't actually low, so why do I feel this way?"

What's important here is that the sensation of 'coldness' we're talking about isn't merely reflected in a thermometer reading. This phenomenon occurs when there's an imbalance between the warmth provided externally by covers and the warmth generated internally by the body itself, which is *nae-yeol* (internal heat).

In Korean medicine, this is understood as a *yang-heo* (Yang deficiency) state. If the body's heat-generating function—that is, the *Gi* (energy) of the Kidneys or the physiological activity of the Spleen and Stomach—declines, then even in a warm external environment, the inside can feel chilly and damp.

I woke up in the middle of the night and feel strangely shivery.

Most people describing these symptoms express it like this: "I woke up, and I feel strangely shivery and cold..." It's common for people to wake up between 2-4 AM, curl up their bodies, or feel even colder after using the restroom.

What we need to pay attention to here is not just the external temperature, but the fact that there is a time when the body's internal rhythm significantly drops. In Korean medicine, this period is seen as the early morning when the Liver and Gallbladder systems are responsible for detoxification and regulation, or when the *Gi* (energy) of the Kidneys is deepest. At this moment, as the internal energy circulation becomes quiet, the production of internal heat temporarily decreases, and the body can perceive this void as a sensation of 'coldness'.

If this continues, could it lead to a serious illness?

Many people are anxious, asking, "If I keep waking up cold, getting chills, then sweating... isn't this a precursor to something serious?" To answer directly, there's no need to immediately suspect a serious illness based solely on this symptom.

However, it's important to note that recurring signals like these could indicate that 'functional boundaries are breaking down.' For example, persistent failure in core body temperature regulation could be a sign of an overburdened autonomic nervous system. If your body temperature repeatedly drops and rises every night, it could signify a distortion in your hormonal rhythms or metabolic patterns.

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Baengnokdam Korean Medicine Clinic, 3rd Floor, Songdo Dream City, 81, Convensia-daero, Yeonsu-gu, Incheon