Not strange at all - the various different sugars and starches eaten are digested - broken down into the simpler sugars., and are then absorbed into the bloodstream, carried around to the liver. If your blood is already carrying enough glucose then the rise in concentration triggers the release of insulin and the liver dutifully stashes away the sugars. You have glycogen, the immediate available and fat, for long term - sort of the RAM and hard disk energy stores. Having rested during sleep - with any luck - you wake and might need to call on stored energy in order to move to where you can get food and water, so the liver reverses the process, releasing glucose into the blood in anticipation of you taking exercise, or possibly needing to evade danger as you go - remember this is the mark one Homo sapiens sapiens we are riding around in, the design is some 200,000 years old.
Disturbed sleep, the start of an illness, even anticipating a stressful day ahead can all trigger even higher concentrations of glucose appearing in order to help to cope with them.