Why did my HRV drop suddenly?

Usually because of last night. Drinks, a late dinner, a hard evening workout, a short night or a cold coming on can each pull HRV down for a night. One low night means little. A 7-day average that stays low is worth acting on.

A sudden drop feels like news about your health. Often it’s news about yesterday. HRV is built to react to what you did, and it does, every night.

Check last night

• Drinks. In 20,968 WHOOP members, one drink more than usual, against one less, came with HRV about 3.8 ms lower in women and 3.3 ms in men. In women, drinking an hour earlier instead of an hour later went with HRV about 1.5 ms higher.
• A hard workout late in the day. In 14,689 people, later and harder workouts came with lower HRV that night.
• Dinner close to bed. In a 7.5-week trial, finishing the last meal 3 or more hours before sleep raised HRV at night.
• A short night. Across 11 trials, sleep loss lowered RMSSD.
• An illness starting. In 2,745 people with COVID-19, heart rate and breathing rate rose and HRV fell.
• A new device or a new spot on your body. A different sensor measures differently. Start a new history.

Why one night means little

Nights swing even when nothing happens. In 10 runners over nine weeks, the weekly average of HRV lined up closely with how much their 10 km time improved. Single days barely did. A 2026 analysis of about 2 million nights from more than 21,000 wearable users found that judging how much HRV varies across a week takes at least five of the seven nights.

What we’d do

Let one night go. Look at the 7-day average. If it sits below your usual range for a week and your sleeping heart rate is up too, take easier days, sleep more and skip the drinks. If you feel ill, or have chest pain, fainting or a racing or irregular pulse, see a doctor whatever the number.