# U-shaped glycemic excursions, and what they are
**URL:** https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771
**Category:** Type 1 & LADA
**Created:** [January 20, 2026, 4:14pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771 "2026-01-20T16:14:25Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@john\_coburg](https://forum.fudiabetes.org/u/john_coburg)
#### Post date: [January 20, 2026, 4:14pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/1 "2026-01-20T16:14:25Z")
Dear all,
Having a horrid day today, and i wonder whether it stems from being high all night. I know we have discussed this ad nauseum, but i remain convinced that recent glycemic history has an impact on future glycemic behaviour. Too many times have i had to double or triple my bolus injection vs normal if i start out high, particularly if I’ve been high for a number of hours, way in excess of whatever extra is needed to bring me down. In any case, i don’t wish to relitigate this as various members were convinced this wasn’t the case (unless anyone has further thoughts), rather I’d like to ask whether people experience U-shaped excursions, typically at night.
I can be bobbing along a little high, just before switching the lights out, when suddenly (usually coinciding with a bolus correction), i stop dropping at a very fast rate. This is annoying, as i either feel i was already headed lower (for whatever reason) and so my additional bolus will cause me problems, so i snack to prevent the forthcoming hypo… or i sleep through it unaware. What typically happens is i spend 30mins or so 2 or 3 mmol/l lower, and then bounce back up as if nothing happened. It can happen multiple times per night - see attachment of last night. I used to think it was just a misreading of my Libre, as they looked too suspiciously ‘clean’…but they happen too often at night to be a random error, so i suspect they’re ‘real’. My questions:
1. Does anyone else experience these U-shapes?
2. What is going on? Are they ‘real’? or just extended (and very unhelpful) glitches?
3. How do you deal with them? See them and strategically ignore? Feels psychologically difficult to ignore a diving level just before going to sleep..
4. Do people find they tend to ruin the next day’s glycemic behaviour? I certainly do…
Thank you for any insights.
EDIT: after multiple boluses with little/no effect, i became suspicious and found a crack in the vial of my Novorapid….which i suspect rendered it inert. Which is interesting in itself.
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### Author:  [@bkh](https://forum.fudiabetes.org/u/bkh)
#### Post date: [January 20, 2026, 4:33pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/2 "2026-01-20T16:33:16Z")
I don’t see any attachment, so I can’t comment based on a graph, but given your description I would consider the possibility of compression lows. Compression lows would not have a U shape, though, they generally would have a narrow v-notch shape, with a fast drop and perhaps a slightly slower recovery when the physical pressure is removed from the sensor.
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### Author:  [@john\_coburg](https://forum.fudiabetes.org/u/john_coburg)
#### Post date: [January 20, 2026, 6:28pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/3 "2026-01-20T18:28:47Z")
thank you ; have added attachment (i find i have to do at home on laptop rather than on phone)
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### Author:  [@Terry](https://forum.fudiabetes.org/u/Terry)
#### Post date: [January 20, 2026, 8:55pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/4 "2026-01-20T20:55:21Z")
Did you confirm the “U-shaped” excursions with a finger-stick? I only ask because I experience similar traces using my Dexcom G6. In my case I’ve found the culprit to be inaccurate sensors.
The excursions at 1:30 am, 3:00 am and 5:30 am were all false lows for me. I use a Dexcom G6. Not every sensor dos this but it is all too common!
65 mg/dL = 3.6 mmolL
120 mg/dL = 6.7 mmol/L
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### Author:  [@jbowler](https://forum.fudiabetes.org/u/jbowler)
#### Post date: [January 20, 2026, 11:23pm UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/5 "2026-01-20T23:23:23Z")
> [@john\_coburg](#):
>
> EDIT: after multiple boluses with little/no effect, i became suspicious and found a crack in the vial of my Novorapid….which i suspect rendered it inert. Which is interesting in itself.
Yes; those excursions are _really_ weird a straightforward (!) tech failure might explain them. I couldn’t deduce what the boluses were from the screenshot; I use xDrip+ myself but I find the lower bar mostly inexplicable.
I do **not** see drop-outs like that; I see drop-outs but they have a different shape and correspond to sensor resets (I use the G7). You have a consistent history of the “U” shaped dropout in that screenshot but I don’t think a crack in a vial of insulin can render it inert, unless you submerge the vial in hydrogen peroxide or the like. If you do the air shots it should be fine.
You are also experiencing a **drop** here; I appreciate that your attempt to do a correction isn’t working (suggesting lack of insulin) but the **drop** suggests a sudden insulin-zap which is gradually reversed.
I’ve never experienced anything like that. I suggest trying to correlate the U-shaped drop-outs with the boluses. Your first U in the top bar correlates with a 3IU bolus _but the second one does not show **any** intermediate boluses_. Perhaps a recording error?
I don’t know why a bolus would record a drop on a CGM which was then immediately reversed. Others: look at the magnitude of the excursions and also their smoothness, for those in the US remember to multiply everything by 18. This is not random CGM artefacts.
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### Author:  [@Michel](https://forum.fudiabetes.org/u/Michel)
#### Post date: [January 21, 2026, 2:23am UTC](https://forum.fudiabetes.org/t/u-shaped-glycemic-excursions-and-what-they-are/15771/6 "2026-01-21T02:23:18Z")
Like @bkh I would possibly suspect pressure lows?