I have slept only less than 4 hours per night for the last year, my circadian rhythm is disrupted and my blood sugar is close to 300 mg/dl. will my blood sugar retutn to normal once i will get a full good night of sleep?

The part of your body that makes the insulin and thus controls the hour to hour blood sugar levels works whether you sleep well or not. You are diabetic until proven otherwise and need effective treatment. Get confirmatory tests and start treatment. Good sleep might improve things slightly, but not enough to end risk of diabetic complications.

A blood sugar this high does meet the definition of diabetes. If you get a better night’s sleep, this will decrease the physiologic stress and will likely decrease your blood sugar levels. But, you should still pursue treatment of your diabetes, even if it is diet control. And, your hemoglobin A1C should be checked with a goal of less than 7, less than 6 if possible. A dietician can be helpful.

Regarding your sleep disorder, this needs a full evaluation, and the institution of a Sleep Hygiene program. Improved sleep will have very little, if any, influence on your blood sugar levels, and you should have this further evaluated also, to assess the extent of potential diabetes mellitus.