If you live with diabetes and wear a continuous glucose monitor (CGM), you’ve probably experienced the mysterious 3 a.m. alarm.
Not 1 a.m., not 5 a.m., always something in the three oh something range. You go to bed with beautifully stable blood sugars, and then, beep, the night suddenly takes a turn.
So what’s really happening at that time of night? Is it your CGM, your hormones, your last meal, or do the diabetes gods simply enjoy keeping us sleep deprived?
Let’s break it all down: what causes those 3 a.m. alerts, how to tell the difference between real and false alarms, and how you can finally get some uninterrupted sleep.
Watch the video or read the article below:
What’s Really Happening at 3 a.m.?
1. The Dawn Phenomenon: Your Hormones Are Waking Up Before You Do
Between 2 and 4 a.m., your body starts preparing for the upcoming day. This is known as the dawn phenomenon.
During this window, hormones like cortisol, growth hormone, and glucagon tell your liver to release glucose so your body has energy to wake up.
People without diabetes release insulin to balance that rise, but for those of us with diabetes, the insulin timing often doesn’t match up.
The result? Your glucose starts to rise, your CGM picks it up, and your 3 a.m. concert begins.
Signs it’s the dawn phenomenon:
- Glucose gradually rises between 2 and 4 a.m.
- It happens consistently, even on days you eat early and don’t exercise late
- The rise looks smooth, not sudden.
Calibration tip (for CGMs that allow it)
- Never calibrate during fast glucose changes.
- Always calibrate when your blood sugars are flat and stable.
- This prevents hours of inaccurate readings.
2. Late Night Meals (Especially High-Fat Foods)
Pizza, burgers, ice cream, chips, and even healthy fats like nuts or avocado digest slowly and can cause delayed glucose spikes.
You might go to bed at 110 mg/dL, but by 3 a.m., that slow-release energy finally hits your bloodstream.
Pair that with an insulin dose that didn’t quite match, and your CGM has plenty to complain about.
3. Basal Insulin Timing and Pump Settings
If you use long-acting insulin (also known as basal insulin), timing matters.
Many basal insulins, including Lantus and Tresiba, have mild peaks. If that peak hits at the same time your body naturally dips overnight, you may experience lows around 3 a.m.
On the other hand, if you:
- Underdosed dinner insulin
- Reduced basal too much
- Skipped a correction
You may see a slow, steady rise instead.
4. Evening Workouts
Exercise, especially resistance training or cardio close to bedtime, can alter overnight blood sugar patterns.
During recovery, your muscles continue to pull glucose from your bloodstream for hours.
This can cause:
- Slow, steady drops overnight
- More nighttime alarms on exercise days
- Greater variability depending on intensity and timing
What I personally do on heavy workout days:
- Adjust long-acting insulin slightly
- Aim to go to bed closer to 140 mg/dL than 100 mg/dL
- Track how different workouts affect my nights (I use my Diabetes Log Book)
Exercise is excellent for blood sugar control, and it should be a part of our daily routine, but it’s helpful to plan for its overnight impact.
5. Compression Lows: When You Roll Onto Your Sensor
A very common cause of nighttime alarms, especially false lows, is compression.
When you roll over in your sleep and put pressure on your CGM sensor, the pressure reduces interstitial fluid flow, making your CGM think your glucose is plummeting.
Once you roll over, the reading jumps right back up.
No, you didn’t almost pass out, you just hugged your CGM a little too aggressively.
How to recognize a compression low:
- Sudden drop with no symptoms
- Sharp bounce back to normal once you move
- The trend arrow doesn’t match how you feel
Quick tip: Always check your trend graph before treating a low. It can save you from overtreating a fake low.
6. Sensor Quirks, Lag Time, and False Readings
Even a perfect sensor can act up under certain conditions.
CGMs measure glucose in interstitial fluid, not blood. This means readings often lag 5 to 10 minutes behind real-time changes, especially if glucose is changing quickly.
Other things that can cause false alarms:
- Temperature changes
- Sweating
- Rapid blood sugar shifts
- Older sensors (especially days 10 to 14)
- Sensor adhesive loosening
How to Treat Nighttime Lows Without Leaving Your Bed
If the alarm is real and your glucose is truly low, you want fast carbs that don’t force you to trek to the kitchen.
Here are my three bedside go tos:
My no-chew quick fixes:
- Fruit pouches are perfect when chewing feels impossible
- Skittles are easy to swallow with water, so you don’t need to brush your teeth again
- Glucose tabs are the fastest and most predictable option
Using the 15 15 Rule
You might want to consider the 15-15 rule for treating low blood sugars.
- Take 15 g carbs
- Wait 15 minutes
- Recheck
- Repeat if still low
Bonus tip: If I go low around 5 a.m., I often need less than 15 g of carbs because morning hormones start raising glucose naturally, and I’m more insulin-resistant at that time. You may see the same pattern.
Tracking what works for you can help prevent rebound highs.
How to Reduce (or Stop) 3 a.m. CGM Alarms
Here are the strategies that make the most significant difference for me and many in the Diabetes Strong community:
- Be thoughtful about sensor placement – Avoid areas you lie on, especially the outer arms.
- Adjust or customize alerts – Use Sleep Mode or gentler thresholds overnight if appropriate.
- Start new sensors earlier in the day – This avoids day-1 wonkiness overnight.
- Be mindful of your dinner timing and insulin dosing – Especially with high-fat or late meals.
- Track patterns – Glucose rises, dips, meals, workouts, basal timing, write it all down. This helps you identify predictable triggers.
- Keep fast-acting carbs at your bedside – It can save you from overcorrecting or stumbling to the kitchen at 3 a.m.
Final Thoughts
Our CGMs don’t hate us. They’re trying to protect us, just sometimes a little too loudly at 3 a.m.
Understanding the patterns behind those alarms can give you more confidence, better sleep, and better overnight blood sugars.
And yes, it will eventually make diabetes feel like it makes a little more sense.
Sweet dreams, and fewer beeps.
