You wake up, check your smartwatch, and notice something annoying. Your resting heart rate—that steady number that usually sits in the 60s—is suddenly creeping into the 70s or 80s. It’s weird. You haven’t started training for a marathon, and you aren't exactly running up a hill while you sleep. So, why is my resting heart rate going up all of a sudden?
Honestly, it’s usually not a "call 911" emergency, but it is a signal. Think of your resting heart rate (RHR) as the check-engine light for your body’s internal systems. When that light flickers, it means your heart is working harder than it needs to just to keep the lights on while you're sitting still. It’s a measure of your heart beats per minute (bpm) when you are at complete rest, typically best measured right after you wake up.
A "normal" range is a wide net, usually anywhere between 60 and 100 bpm. However, if you're used to a 55 and you're now seeing a 68, that’s a trend worth looking at. It's about the deviation from your baseline, not just the number itself.
The invisible drain of stress and "over-functioning"
Life is heavy right now. We don't always give credit to how much mental load translates into physical strain. When you’re stressed, your body dumps cortisol and adrenaline into your bloodstream. These hormones are basically "go-juice" for your heart. They tell your heart to beat faster and harder because your brain thinks you might need to fight a bear or run away from a falling rock.
Except there is no bear. There’s just an overflowing inbox or a tight mortgage payment.
Chronic stress keeps your sympathetic nervous system—the "fight or flight" side—in the driver’s seat. This prevents your parasympathetic nervous system (the "rest and digest" side) from taking over. If you never truly relax, your heart never truly slows down. It’s like idling a car at 3,000 RPMs instead of 800.
Poor sleep isn't just about feeling tired
If you aren't sleeping well, your RHR will climb. Period. During deep sleep and REM cycles, your heart rate should drop to its lowest point of the day. If you’re tossing and turning, or if you have undiagnosed sleep apnea, your body stays in a state of high alert.
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According to the American Sleep Association, sleep deprivation triggers an immediate uptick in blood pressure and heart rate. Even one night of "trash sleep" can cause a noticeable spike the next morning. If this becomes a pattern, your baseline shifts higher, making your heart work overtime 24/7.
Dehydration and the "thick blood" problem
This is a big one that people overlook. Your blood is mostly water. When you’re dehydrated, your total blood volume actually decreases. This makes your blood thicker and harder to move through your veins and arteries.
To compensate for the lower volume, your heart has to beat more frequently to deliver the same amount of oxygen to your brain and muscles. It’s a simple math problem for your body. If each pump moves less liquid, you need more pumps per minute.
You’ve probably felt this after a night of drinking. Alcohol is a double whammy: it dehydrates you and it’s a toxin that your heart has to work hard to process. If you’re wondering why is my resting heart rate going up after a few Friday night cocktails, there’s your answer. Your heart is basically doing cleanup duty while you sleep.
The "pre-sick" spike and immune response
Sometimes, your smartwatch knows you’re sick before you do.
When your immune system detects a virus or bacteria—even if you don't have a fever or a cough yet—it kicks into gear. This metabolic spike requires energy. Your heart rate rises to transport white blood cells and nutrients to the front lines of the infection.
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I’ve seen plenty of people track their data and realize their RHR jumped by 10 beats the day before they tested positive for the flu or COVID-19. It’s a fascinating, if slightly creepy, early warning system. If your heart rate is climbing and you feel "off," your body might just be fighting a war you haven't felt yet.
Overtraining and the "athlete’s trap"
There’s a common misconception that more exercise always equals a lower heart rate. While that’s true in the long run, in the short term, overtraining will send your RHR through the roof.
If you hit the gym too hard and don't allow for recovery, your nervous system gets fried. This is known as Overtraining Syndrome (OTS). One of the primary clinical markers for OTS is a persistent increase in resting heart rate. It’s your heart’s way of saying, "Hey, I’m still tired from yesterday, can we please chill?"
Professional athletes and coaches, like those at Performance Health, actually use RHR as a metric to decide if a player should train or rest. If the RHR is up by more than 5 beats from the average, it’s usually a rest day.
Medications and "hidden" stimulants
Check your medicine cabinet. Are you taking something new?
- Decongestants: Many over-the-counter cold meds contain pseudoephedrine, which is a stimulant.
- Asthma inhalers: Some bronchodilators can cause a racing heart.
- ADHD medications: Stimulants like Adderall or Ritalin are notorious for bumping up the RHR.
- Thyroid meds: If your dose is slightly too high, it can mimic hyperthyroidism, sending your heart into overdrive.
Even "natural" supplements can play a role. If you’re taking a new pre-workout or a fat burner, check the caffeine content. Some of those contain upwards of 300mg of caffeine—the equivalent of three or four cups of coffee—in a single serving. That will absolutely move the needle on your heart rate.
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When should you actually worry?
Most of the time, an uptick in RHR is a lifestyle signal. It’s a prompt to drink more water, go to bed earlier, or stop stressing about that email. But sometimes it’s more serious.
If your resting heart rate is consistently above 100 bpm, that’s a condition called tachycardia. If this is accompanied by palpitations (feeling like your heart is skipping a beat or "flopping" in your chest), dizziness, or shortness of breath, you need to see a doctor.
Conditions like anemia (low iron), thyroid imbalances, or even underlying heart rhythm issues like Atrial Fibrillation (AFib) can cause your RHR to climb. It’s not about being paranoid; it’s about being informed. A simple blood test or an EKG can usually clear things up pretty quickly.
Actionable steps to bring it back down
If you’ve ruled out a medical emergency and you just want to get your numbers back to a healthy baseline, you have to play the long game.
- Hydrate like it’s your job. Aim for half your body weight in ounces of water daily. It’s the easiest way to lighten the load on your heart.
- The 4-7-8 Breathing Technique. This isn't woo-woo science; it’s physiology. Inhale for 4 seconds, hold for 7, exhale for 8. Doing this for just two minutes can manually "flip the switch" from your sympathetic to your parasympathetic nervous system.
- Cut the "hidden" stimulants. Watch out for soda, dark chocolate late at night, and those "wellness" shots that are secretly loaded with caffeine.
- Prioritize the "cool down" period. Stop looking at screens an hour before bed. The blue light and the dopamine hits from social media keep your brain (and heart) in an active state when they should be winding down.
- Track the trends, not the moments. Don't freak out because your heart rate is high for ten minutes. Look at the weekly average. That’s where the real story lives.
Your heart is a muscle, and like any muscle, it gets tired. If you're seeing your resting heart rate go up, treat it as a conversation. Your body is asking for a little more grace, a little more water, and maybe a few more hours of shut-eye. Listen to it.