Scary nighttime lows

Things that go beep in the night

It’s 3 AM. Your phone is buzzing somewhere on the nightstand. You squint at the screen, and it says LOW.

Your brain isn’t awake yet. You try to remember what you ate, when you last took insulin, and whether today was a busy one, and none of it comes right away. That’s what makes overnight lows so scary: you have to figure out which kind this is while you’re still half-asleep.

Four nights that scared me, and the moths that pull the same tricks. Some look like trouble and aren’t; some do their damage where you can’t see it.

Seeing a number that low is so scary. Every instinct says to treat it, but you know you shouldn’t.

My night

I was steady around 100 to 115 for hours. Around 12:45 AM, the line dove to two readings under 50. By about 1:05, I was back at 110, as if nothing had happened.

In late summer, something that looks like a yellowjacket rests on the raspberry leaves. It’s a raspberry crown borer, Pennisetia marginata, a moth dressed as a wasp. The giveaway is its feathery antennae (UC IPM). A compression low pulls the same trick: it looks like danger, and the fingerstick is how you check the antennae.

What’s going on

A CGM reads the fluid between your cells, not your blood. When you lie on the sensor, the pressure squeezes that fluid away from the filament, and the reading drops. If nothing in your day explains the low, that’s your first clue it isn’t real.

It drops fast, and your heart drops with it. Then it’s over.

My night

I was in range all evening. A little before 9 PM, I slid under 70 and bottomed out around 60. I treated it, and after about 25 minutes under 70, I was back up. Within half an hour I was near 110, and I stayed in range the rest of the night.

The hummingbird clearwing, Hemaris thysbe, is a moth that flies by day. It hovers at flowers like bee balm and coneflowers, stays at each one only a moment, and darts off (UW–Madison Extension). This low is like that: here, then gone.

What’s going on

This one is real, but it’s quick. Treat it, recheck, and it’s done. The work is making sure it really is done before you go back to sleep.

“Even once treated, I thought everything was good to go back to sleep. I had no idea I had been low so long.”

My night

I hovered right around 70 all evening, and the low alerts kept coming. Just before midnight I slid into the low 60s and got an urgent low alert. By about 12:40 AM I was back up near 100.

I thought I had enough, but should have continued treating. It drifted right back down, and by 1:30 I was under 70 again. I stayed in the 60s until almost 3 AM.

The five-spotted hawkmoth, Manduca quinquemaculata, is the adult tomato hornworm. The caterpillars blend into my tomato plants so well that I usually find the stripped stems before I find them (UMass Extension). This low works the same way: by the time you see the damage, it’s been at it for hours.

What’s going on

This one is real. A more active day can keep lowering your glucose for hours afterward; in one small study, lows clustered 8 to 12 hours after evening exercise. Lantus, a long-acting basal insulin, keeps working at the same pace, so a treated low can come back while you sleep.

The numbers don’t agree, and you have to pick one to believe.

My night

My Dexcom kept reading lower than my meter. At 9:11 PM, it said 55 and my meter said 69. Eleven minutes later, it still said 55, and my meter said 87.

I calibrated four times that night. Each time, my meter came in 14 to 32 points higher than the sensor.

The tomato fruitworm, Helicoverpa zea, bores into tomatoes, and sometimes peppers (Oklahoma State Extension). The fruit looks perfect until you cut it open. A number can be like that: clean on the screen, with the problem inside.

What’s going on

Either number can be wrong. Unwashed hands can make a meter read high, and a sensor can be off on its first day or when you’re lying on it.

The takeaway

Check before you treat. Treat a real low fast. Bring the patterns to your care team. And maybe sleep on the other arm.

Happy Halloween.