January 31, 2025

We all know the feeling: You’re more tired than usual, you can only breathe out of one side of your nose, you can’t stop coughing and your head is throbbing.

Yep, you’re probably getting sick — and some of the metrics measured by your compatible Garmin smartwatch might echo how you’re feeling.

First things first: Your Garmin smartwatch is not a medical device. Your watch cannot tell you if you’re sick, and you should not use it to determine if you’re sick. If you’re worried about your health, you should talk to a doctor. Garmin smartwatches and the data they provide are not intended to diagnose, treat, cure or prevent any disease.

Still, understanding how your body might react when you’re sick can be helpful.

What happens when you’re sick?

Not everyone’s body works the same way, and some diseases and conditions may affect how the body reacts to illness. Typically, at the onset of getting sick, your body begins an immune response to help fight off the illness and recover. This immune response may place your body under stress.

Your body’s autonomic nervous system (ANS) regulates a variety of automatic functions including your heartbeat, according to Cleveland Clinic. The ANS is the umbrella over the sympathetic (fight-or-flight stress response) and parasympathetic (rest and digest) nervous systems. These systems affect your heart rate and heart rate variability (HRV), which is the varying time between heartbeats.

A sympathetic nervous system response may mean your body is under stress. Stress and exercise may raise your heart rate, which could cause your HRV to drop. If you get a fever, for example, your body may start an immune response and become stressed. Even a slight  increase in body temperature can raise your heart rate by 7 beats per minute, according to a study published in the National Library of Medicine. Studies also found an association between various infections and lower HRV levels and increased heart rate.

When your parasympathetic nervous system takes over, your body may be resting and recovering. This could cause your heart rate to go down and your HRV to increase.

What Garmin metrics are based on HRV?

Garmin watches track a variety of health and fitness metrics, including HRV¹. Your heart rate and HRV are related to your sleep, stress level and Body Battery™ metrics on your compatible Garmin watch.

Garmin sleep coach¹, for example, uses your HRV — as well as your age, activity history, sleep history and naps — to recommend how much sleep you need. Lower HRV levels may be a sign you need more sleep to help you recover.

With Garmin stress tracking¹ estimated by the Firstbeat Analytics™ engine, you can make sense of your heart rate and HRV data by learning how your body responds to different stressors.

If your Body Battery is struggling to charge, for example, it could be because you’ve increased your physical activity, you haven’t slept well, you drank alcohol, or you might be getting sick.

Understanding how the human body typically reacts to stressors is one way to build up your health awareness. Garmin smartwatches track a variety of health and fitness metrics that can support a healthier lifestyle.

Browse Garmin’s collection of fitness and health tracking products to start your health journey today.

_{¹See Garmin.com/ataccuracy}