Ketones are always present in the human body (unless you are one of the few people with an inherited metabolic defect that prevents their creation).
The overnight tracing of my BG (above) was made possible in part by the ability to generate enough ketones overnight to lighten the load on my body's need to generate sugar to fuel my sleeping body many hours after my last meal.
This is just normal human biochemistry . But we are often taught to malign the ketone. The ketone is not bad. The ketone is our friend in many ways. I write about this in my book Sugar Surfing.
Ketones are an energy source. I suppose if glucose is high octane gasoline, the ketones are like diesel. They are a complementary forms of useable bioenergy.
In great excess, like in diabetic ketoacidosis (DKA), the ketone can be harmful in some ways just as drinking too much water all at once or breathing 100% oxygen for extended periods of time can kill a person, too.
Ketones fall into that large group of things which are best taken "in moderation".
My overnight BG is in part due to being basal neutral with my Tresiba insulin dose, plus allowing ketones to support my energy needs and spare the excess consumption of sugar (glucose). If my basal insulin were too high it would act to suppress the normal creation of these vital ketones and cause me to have a higher risk of low blood sugar during the night.
Read more about ketones in the book.