A demanding week, poor sleep, stress, or a busy schedule can leave almost anyone exhausted.

But persistent fatigue that doesn't improve with adequate rest can sometimes be associated with thyroid dysfunction.

When thyroid hormone levels are too low, many body processes slow down. A person may feel:

• Constantly tired

• Sluggish

• Physically weak

• Mentally foggy

• Less motivated

• Sleepy during the day

Some people describe it as feeling as though their body is operating in “slow motion.”

Hyperthyroidism can also cause fatigue, although the experience may be different. Someone with an overactive thyroid may have difficulty sleeping, feel restless, or experience muscle weakness, eventually leaving them exhausted.

Because fatigue is extremely common and has countless possible causes, it shouldn't automatically be blamed on the thyroid.

Persistent fatigue deserves evaluation when it interferes with everyday life.

3. You Suddenly Feel Much Colder—or Much Hotter

The thyroid plays an important role in regulating the body's energy use and heat production.

As a result, changes in thyroid function can influence how you perceive temperature.

With hypothyroidism

You may find yourself unusually sensitive to cold.

You might notice that:

• Other people are comfortable while you feel cold.

• Your hands and feet seem colder than usual.

• You need extra layers of clothing.

• You feel chilled even in relatively mild temperatures.

With hyperthyroidism

The opposite may happen.

You may:

• Feel unusually hot

• Sweat more than usual

• Have difficulty tolerating warm rooms

• Wake up sweaty

• Feel uncomfortable in temperatures others consider normal

Again, temperature sensitivity has many potential causes.