Any illness will put up your Bg levels. Even some painkillers can do that too. It will settle back down once you are feeling better........try not to worry too much about this.
I had over 6 months of Bg levels being massively high and then low (24 - 2.9) due to Cancer and the treatment I was put on. That treatment and the illness are now finished, hopefully.....blood sugar levels all getting back to normal without much of a change in my HbA1c levels and no ill effects. Sometimes the Diabetes (or pre diabetes) has to take a back seat.
Ken