A diabetic patient who always have sudden drop in blood glucose

My dad is a 56 y/o diabetic patient with high blood glucose level for quite a while and then he finally accepted my convince to go see a doctor and started to control his blood glucose level… but ever since he started to take the medication and limit his sugar intake, he always have the problem where his blood glucose level will suddenly drop from a high level to a normal level that makes his body cannot get used to it… then he’ll feel hungry, no energy and felt fainting, sometimes blackout… this usually happens during midnight (sometimes during daytime as well) when everyone is a sleep but then he got up to eat and wakes us up for help as he has no energy to make a food on his own. We got back to his doctor during the first time when he felt fainting and blackout. The doctor told us that it was due to his blood glucose level suddenly drop from a high level to a normal level that makes him can’t get used to it.

May I know what might be the cause for this sudden drop? He do a lot of heavy work and sweat a lot everyday… is it that he did too much work that causes his glucose level used up already?

Do you have any suggestion that he can do to actually control his blood glucose level slowly back to a normal level? because if he kept on having this problem, it will be very dangerous if he was driving on the road.

Thank you for your help.