Feeling tired and feeling cold often arrive together.
That does not mean fatigue always causes coldness directly.
A big part of the connection comes from the body’s normal daily temperature rhythm.
Body temperature changes across the day
Core body temperature is not perfectly constant.
It rises and falls on a roughly 24-hour schedule.
As bedtime approaches, core temperature usually begins dropping.
That decline is one of the biological changes associated with preparing for sleep.
Sleepiness often appears at the same time
Because the temperature decline and increasing sleepiness are both connected to circadian timing, you may notice them together.
Late at night, you are tired.
You also feel colder.
The two sensations share a schedule.
What does sleep deprivation do?
Not getting enough sleep can interfere with several parts of normal physiological regulation, including temperature control.
The exact response varies by person and situation.
It is safer to say sleep loss can make temperature regulation less efficient than to claim tiredness always drops body temperature by one fixed amount.
Why does a blanket help you fall asleep?
Warm skin can actually support the process of losing heat from the body’s core.
That sounds backward, but warm hands and feet can help blood carry heat toward the skin where it can leave the body.
That is one reason getting comfortably warm can make sleep easier.
Is this related to shivering?
Only indirectly.
Shivering is an active emergency response that produces heat when the body is getting too cold.
Feeling chilly when sleepy usually occurs long before the body needs that kind of response.
When is feeling cold not about sleep?
Persistent unusual cold intolerance can have many other causes, including anemia, thyroid problems, low body weight, illness, or medication effects.
Fatigue plus coldness is common, but it is not automatically a sleep explanation.
Sometimes tiredness and coldness simply arrive together because both are tied to the body’s daily temperature rhythm.
And that’s the short explanation.
Related explanations: Why do we shiver when cold?, Why can a fever make you feel cold?, and Why is it hard to fall asleep sometimes?