You fall asleep at a decent time.
You’re in bed long enough.
But the next morning:
HRV is lower than usual
Resting heart rate is higher
Recovery feels incomplete
One common culprit?
Late-night screen exposure.
Even when sleep duration looks okay, what happens before bed can strongly affect how well your nervous system recovers overnight.
Light at Night Confuses Your Internal Clock
Your circadian rhythm relies on light to know when it’s day and when it’s night.
Bright screens — phones, tablets, TVs, laptops — emit light that tells your brain:
“It’s still daytime.”
This suppresses melatonin, the hormone that helps your body shift into sleep and recovery mode.
When melatonin release is delayed:
Sleep onset can be pushed later
Deep sleep may be reduced
Parasympathetic recovery is less effective
Blue Light and Nervous System Activation
Screens don’t just affect hormones — they affect the nervous system.
Late-night screen use often means:
Scrolling
Responding to messages
Watching stimulating content
Working
This keeps the brain engaged and the nervous system in a more activated, alert state.
Instead of downshifting into parasympathetic dominance before bed, your system stays partially “on.”
That can lead to:
Higher nighttime heart rate
Lower HRV overnight
Less complete recovery
Sleep Duration vs Sleep Quality
You might still sleep 7–8 hours.
But if melatonin timing is off and the nervous system stays more activated, sleep can be:
Lighter
More fragmented
Less restorative
HRV reflects the quality of recovery during sleep — not just how long you were in bed.
That’s why late screen use can show up in morning recovery data even when you “slept enough.”
The HRV Link
When pre-bed light and stimulation delay the body’s transition into recovery mode, the parasympathetic nervous system has less time to fully dominate overnight.
This often shows up as:
Lower HRV
Higher resting HR
A feeling of incomplete recovery
Over time, inconsistent sleep timing from late screen use can make HRV trends more erratic.
Simple Ways to Reduce the Impact
You don’t have to eliminate screens completely.
But you can reduce their recovery cost:
• Stop bright screen use 60–90 minutes before bed when possible
• Use night-shift or blue light–reducing settings in the evening
• Lower screen brightness at night
• Replace some screen time with low-light, low-stimulation activities (reading, stretching, quiet routines)
The goal is to give your nervous system a clear signal:
The day is ending. It’s time to recover.
The Big Takeaway
Sleep isn’t just about how long you’re in bed.
It’s about how well your nervous system can shift into recovery mode overnight.
Late-night screen use can delay melatonin, keep the brain stimulated, and reduce parasympathetic recovery — leading to lower HRV the next morning.
Protecting the hour before bed often improves recovery more than adding extra recovery tools.
Sometimes better sleep starts with putting the phone down a little earlier.