Some fluctuation after eating a meal is normal, but your dad's blood sugar doesn't seem like it's done that much in the past. Even so, people's "normal" levels and ranges can change with time, and that might be happening here. I would give this one more week to see if his insulin levels even out and the fluctuations stop. If it keeps up, call his doctor and move up the appointment. Something like this shouldn't wait several more months. If his sugar dips to 30 again- take a trip to the ER. A level that low is dangerous. Even if he has recovered quickly before, there's no guarantee he will every time; he could easily bottom out.

As to his doctor- I've seen how *not* easy it is to get an older person to change doctors. Try talking to him and see why he's so adamant about not changing doctors. Also, try calling the office yourself to talk to the doctor (or one of the office nurses- an invaluable liason/tool sometimes). Tell him your concerns, and see if there's a reason he's been treating your father as he has. It could be that he's afraid of insulting a long time patient, or your dad may have forgotten to tell him everything during his previous visits. If Doc doesn't seem responsive to your concerns- or your dad's change in insulin levels- try again (and again, etc) to change doctors. Not doing so could be detrimental to his health. Good luck!~