Hi Jan…yes and yesterday afternoon and early evening was a perfect example. Sometimes it happens when I am close to changing my infusion set (Medtronic 670G) like yesterday. My BG rose to 220 without having eaten anything for several hours. I bolused and bolused but continue to rise to 290. Changed my infusion set and finally around 9pm I started to fall and by midnight down to 160. Woke up at 120 and so far today totally normal. What sucks is you start to think something is wrong with the pump or have I become insulin resistant etc. No doubt the absorption rate decreases in the final day of an infusion set at least for me. After reading the responses I believe you are not using a pump. I agree in general with what one poster stated…the highs and lows of a type 1 diabetic sometimes makes NO sense! Hope you are having a great weekend Jan!
Thanks for the response. And no, I am not using a pump, which I just figured out is MDI. 
I’ve only been on CGM for not quite 2 months now, despite being Type 1 for 40 years (1979). So, I have quite a lot to learn. I appreciate your experience, and am finding out that there’s a lot of stuff going on that I never knew about!
One other thought Jan…when I forget to bolus 15 minutes prior to eating (especially a higher carb food like French fries) I have the same experience where it seems like bolusing doesn’t work very effectively. Tonight I had a good batch of fries…was at 148 when I bolused 15 minutes before eating the fries, and 2 hours later I am at 101. Are you considering going to a pump?
I don’t sweat 200 for a day. Neither does my endo.
@coolone58 - I’m learning about the wait time after taking a shot. It seems to be subjective, which as a scientist is difficult for me. I want a rule to use, like take the number of carbs and multiply by 10 to find the minutes to wait. I do know to wait longer when I’m higher and wait less when I’m lower.
Right now I’m taking one step at a time, and am learning as much as I can from CGM, but not considering a pump right now.
@SteveMann - Thanks for your input, it’s good hear the “rules” others use. I tend to be a perfectionist, which wasn’t such an issue pre-CGM when I happily went along not knowing all the things I know now are going on, i. e. at night and between finger sticks.
We’ve found with our 11 yo daughter that jumping on a mini trampoline for just 5 minutes seems to get the insulin working if she’s not coming down.
It’s not the number of carbs. The main thing is the expected speed of digestion. We want to match the speed of the the insulin working to the speed at which digestion will release glucose into the bloodstream. Complex foods with protein and fat tend to digest slower, so to slow down the insulin we don’t give it way ahead, and maybe we only give part to start, and more after a while (the “split bolus” technique.) Simple carbs (mostly sugars) digest quickly, so will tend to spike the BG, so we want to give the insulin earlier to help it get started and build up a bit before the flood of glucose hits, and maybe we only want to eat some of those carbs, wait for the insulin to catch up, and than eat the rest of the carbs (I call this the “split carbs” technique, but nobody else uses that term.)
Some people like the book “Sugar Surfing” by Dr. Stephen Ponder, which gives lots of examples of reading CGM graphs and deciding on insulin and carb correction strategies to steer the BG in a good direction. It is more applicable to pumpers than those on multiple daily injections (MDI) but the concepts apply in either case.
I have never heard of another diabetic who uses the mini-trampoline as part of the strategy. I’m also a jumper, and I also find just 5 minutes to do the trick! 
I have found that on those ridiculously annoying days that bolusing corrections does NOT work unless I use an elevated TB, like + .025% or more. but I can do it easily through my pump. I suppose that you could just increase your Lantus???
I had this happen recently; for 2 days I needed 110% TB to stay in range, and now, a few days later, I am on 97% TB and am in range.
here’s the deal: you are NOT alone!!! wishing I had the magic wand to wave over all of us.
there are so many reasons that this can happen: sleep/stress/ emotions/ exercise/ hormonal/ headaches, etc.
@daisymae Thanks for the input. Increasing Lantus obviously isn’t immediate, and I take it at night, so not much use for highs that sneak up suddenly. I have used a 15 or so minute walk (even around the house) and sometimes that helps.
I do this too. only I do mine around the living room for 1/2 hour. my husband comes with me 
I live on the top floor of a four-storey walkup, and I find climbing the stairs a couple of times has the same effect. Bonus points for getting a load of laundry started in the basement.
Yes, I’ve had many of days above the 200 mark and have taken one or two units of Novolog above my normal to combat it. One way I can cut down my bg is some physical activity over an hour. Usually I walk - rain or shine. Not always convenient and I have seen it creep back later in the day. These odd high days usually only last a day or two and my endo didn’t seem overly concerned.
Around the holidays, often.
I try to go to bed with my BG reading 150. I’ll wake in the morning with a BG around 80-100.
Sometimes, around the holidays, I just can’t stop myself from taking just one more cookie. My wife makes the most delicious cookies. Fortunately just around the holidays.
If my BG is over 250 at bedtime, I will inject more Novolog according to my coverage formula that my Endo prescribed.
I have this problem too, and can’t understand why the 200 to 220 level seems to be the hanger. I never have a 150 that hangs for hours. I currently mostly blame infusion sites nearing the end of my second day, or dehydration. Always check with a fingerstick to make sure it isn’t a Dexcom G6 problem, but it usually is not. I use bike riding to bring it down, or pump more insulin and try to catch the low if the bolus succeeds and I come crashing down. Wonder if the Tandem loop update will address this problem. Meantime maybe I need one of those mini-trampolines.
If I go to bed at night with a BG of 150, I wake with a BG near 100.
I get the same numbers. I think there is some metabolic happening. I do, sometimes, flatline at 150 but it is mostly during the day and it’s balancing on a tightrope, not grounded on an infinite plateau.
Most of my recent experiences have been overnight, they have I think invariably been associated with protein/fat (cheese, nuts) which I regularly snack on later in the day.
This is some weird sort of stasis; since I use a CGM I will wake up periodically and do a bolus, but it doesn’t seem to change anything until the morning (when I arise from my bed). I don’t hit 300 and I don’t go below, maybe, 190.
I suspect there is some complex interaction with the changes of my metabolism because of sleep and with gluconeogenesis, but I don’t have the faintest idea what. There is, for certain, a PhD thesis here.
Oh, I drink, so ethanol is another spanner in the works.
Today’s high was due to insulin going bad in the pump. I can use it for about six days, but today was the seventh, and the insulin dropped to about half effectiveness if that. When I refilled the reservoir with new insulin everything returned to normal. But this was not a 200 to 220 hang. It rose well beyond 220 before I realized that it was not the pump, not the cgm, not the infusion site but actually the insulin.
And thanks to @jbowler for the word that describes how the body makes glucose out of fat or other non-carbohydrates. I have always known that was happening, and it was part of the reason I resisted using carbs for bolusing–carbs alone don’t tell the whole story. I had to convert to carb bolusing to be ready for the Tandem pump update.
I don’t understand. Do they prevent an extended bolus when Control-IQ is running? Years ago with a t:slim I tried T.A.G. bolusing (“total available glucose”) using an extended bolus with the carb grams given immediately, and 40% of the protein grams plus 10% of the fat grams given over 5 hours.