It's because ur sugars rise naturally during the night. Also u probably eat ur main meal too close to bedtime & there may be too many hidden sugars in ur diet. The best time for diabetics to eat their main meal is from 12-1pm midday then ur sugars will have stabilised by bedtime. A snack of sugar free foods @5.30pm and nothing to eat after 6pm. A long brisk power walk or jogging after ur main meal with stabilise & help lower ur blood sugars