I used a continuous glucose monitor (CGM) for several months to better understand why I hit a wall each afternoon—around 3–5pm—when my energy, focus and motivation would nosedive. The CGM didn’t magically fix everything, but it gave me precise, minute-by-minute feedback that turned vague feelings into actionable patterns. If you get a similar late-afternoon crash, reading your CGM can help you identify causes and try targeted fixes that actually work.
Why a CGM is useful for afternoon crashes
A CGM shows you how your glucose responds to meals, snacks, caffeine, movement and stress. Unlike a single finger-prick test, it reveals the trend—whether glucose is rising, stable or falling—and the speed of that change. For late-afternoon crashes, it’s often not the absolute number that matters but the direction and the rate of change. A fast decline from a high post-meal peak can create a rebound low (or a sensation of low energy) even if your glucose remains in a “normal” range.
Key patterns to look for
When I began, I specifically watched for these patterns. You can check your CGM for the same.
How I tracked and annotated my CGM data
I treated the CGM like a lab notebook. Every meal, snack, nap, walk, coffee and stressful call got a timestamp in the app notes. After a week, I replayed the days to see what reliably preceded that afternoon slump.
This contextual info helped me link behavior to the glucose line. For example, a pasta-heavy lunch + no post-meal walk = a 60–80 mg/dL spike then a fast drop to feelings of fatigue. A protein-focused lunch + 10-minute walk = a mellow curve and steady afternoon energy.
What glucose numbers mean for energy (simple guide)
Everyone is different, but here’s a practical table I used to interpret readings in relation to how I felt:
| Glucose range (mg/dL) | Typical feel | What to watch |
|---|---|---|
| 70–90 | Sometimes low energy, light-headed if trend is down | Watch for downward arrows; need stabilizing snack if falling |
| 90–140 | Stable energy for most people | Ideal window; avoid large spikes that precede falls |
| 140–200 | May feel foggy or tired especially after a sharp rise | Large swings common; prefer smaller, more balanced meals |
Practical fixes I tested that helped
After identifying patterns, I experimented with specific strategies and used the CGM to compare outcomes. These are the ones that consistently reduced my afternoon crash:
How to decide when to snack (using the trend)
Instead of snacking on a schedule, I started snacking based on the CGM trend arrow:
Special considerations
Some situations need extra caution:
Tools and apps I used
I used a Dexcom sensor paired with its app for continuous trend arrows and alerts, and sometimes wore a FreeStyle Libre to compare. The Dexcom trend arrows were especially helpful for deciding whether to act immediately or wait—two arrows down (fast fall) meant act; one arrow down (slow) meant monitor and consider a small snack.
How to test changes and keep improving
Make one change at a time and track for a week. For example:
Over several weeks, you’ll discover which levers—meal composition, portion size, timing, or movement—affect your afternoon energy most. The CGM’s value is rapid feedback: you don’t have to guess whether something worked; you can see it.
Reading your CGM isn’t about chasing perfect numbers. It’s about learning the rhythms of your body and using that knowledge to make simple, practical adjustments—so you can get through the afternoon without the usual slump and maintain steady focus until the end of the day.
