High blood sugar can make you feel more thirsty, tired, frequently urinate, headache, and blurry vision. If left untreated, you may experience abdominal pain, fruity-smelling breath, nausea, vomiting, shortness of breath, fast and deep breath, dry mouth and skin, flushed face, muscle aches, weakness, confusion, and unconsciousness.
Reference:
CDC: https://www.cdc.gov/diabetes/managing/manage-blood-sugar.html
Mayo Clinic: https://www.mayoclinic.org/diseases-conditions/hyperglycemia/symptoms-causes/syc-20373631