A variety of things can trigger an increase in blood sugar level in people with diabetes, including: stress an illness, such as a cold eating too much, such as snacking between meals a lack of exercise dehydration missing a dose of your diabetes medication, or taking an incorrect dose over-treating an episode of hypoglycaemia (low blood sugar) taking certain medicines, such as steroid medication Occasional episodes of hyperglycaemia can also occur in children and young adults during growth spurts.