If your blood sugar is normally high and your medication stabilizes it quickly, will you feel negative effects?

This is normal. His body was used to feeling the way it did when the sugar levels were higher. The body will adjust, it may take a few weeks. I felt the same way, and many diabetics I know told me they had the same thing happen to them. Talk to the doctor, there may be something he can take for the eye pain, but generally doctors do not like to give medications for this, because it will p soon. If his hands and feet continue to have a lot of pain, his doctor may prescribe something like Cymbalt, or Lyrica, but they do not completely stop the pain and do have some nasty side effects. Tell your dad to be patient, he will feel much better soon.