Symptoms of hyperglycaemia in people with diabetes tend to develop slowly over a few days or weeks. In some cases, there may be no symptoms until the blood sugar level is very high. Symptoms of hyperglycaemia include: increased thirst and a dry mouth needing to pee frequently tiredness blurred vision unintentional weight loss recurrent infections, such as thrush, bladder infections (cystitis) and skin infections Symptoms of hyperglycaemia can also be due to undiagnosed diabetes, so see your GP if this applies to you. You can have a test to check for the condition