Known as dawn phenomenon when it happens in the mornings. Basically your liver thinks you need more glucose and dumps a load into your blood for you. It happens for a few reasons.
In the mornings it is thinking you need the energy to get up and going. Breakfast if you like. It does improve somewhat with time if levels remain great the rest of the day but I’m talking months not days. It’s usually the last reading of the day to do what you want it to do.
After a fasted period it might believe you’re starving and do likewise if it’s used to experiencing higher levels than you currently have. It’ll get used to normal levels in time and behave better without the panic.
Same after some exercise. It thinks you need more energy and boosts you whether you need it or not.
And then longer term mornings can remain the highest of the day even after the dawn phenomenon eases if you are very low carb. Then it’s called adapative glucose sparing and isn’t considered a problem as its physiological insulin resistance caused by the (intentional and beneficial) lack of glucose rather than pathological caused by disease (Type 2)