The critical problem caused by all types of diabetes comes down to the same thing. All systems in the body are starving to death. They are not getting the sugar they need to do their work.
The fundamentals are pretty simple. When you eat something your digestive track processes that into sugar. Glucose to be specific. That Glucose gets passed into the blood stream and gets picked up by and connected to a red blood cell. It takes one molecule of Insulin to get one molecule of Glucose to detach from a red blood cell and be available to a muscle or organ cell for use.
In the case of Type 1 diabetes the pancreas is no longer creating Insulin or the body is unable to use the pancreas has created. The body's immune system has attacked the beta cells in the pancreas. It is the beta cells that make Insulin. That means it is impossible for a sugar molecule to release from the red blood cell. That means none of the bodies cells are getting fed to the degree they need food.
In the case of Type 2 diabetes the pancreas is no longer making enough Insulin. That means not enough of the bodies cells are getting enough to eat.
In either case you have body cells with out food. Those cells respond by seceding a chemical that tells the system "Hey, we are hungry down here!". The system reacts in a number of ways.
One of the main things that takes place is the liver releases a shot of glucose into the circulatory system from its private reserve. This adds more sugar molecules to the blood cells. Since there is little or no Insulin to get the glucose off of the blood cell the Diabetics blood sugar level rises.
It is impossible for the sugar to get off of the blood cells and get to the cells that need to eat. The cycle just keeps repeating and repeating and repeating. A diabetic's blood sugar level just keeps getting higher and higher.
Other body systems kick in. They cells are screaming "Give us food!". Pretty soon the diabetic is feeling hungry. It the diabetic succumbs to this feeling and eats, then the blood sugar level goes even higher.
The liver's private reserve of glucose can also get used if the body gets into the "Fight or Flight" mode. If a diabetic gets into a hectic situation, one of the things that happens is the liver dumps glucose into the blood stream so the muscles will have the fuel to do what they need to do. A diabetic's blood sugar level just keeps on rising.
In the short term nothing really significant happens. If you recall the last time you over indulged at a Thanksgiving dinner you will get the idea. You felt lethargic, a little sleepy and probably spent a few hours sitting on the couch watching a sports event. Your upper level brain functions shut down to some extent. It was OK to be a couch potato. That is what a person with uncontrolled diabetes feels like much of the time. Only you need to turn up the volume two or three times.
The long term effects are where diabetes becomes quite wicked. High blood sugar will damage your nervous system, kidneys, heart, feet, eyes and more. It can lead to strokes, heart attacks, kidney failure, blindness, amputations and more.
There is a way to slow down the ravages of diabetes. It will even work to prevent the original on set of diabetes. It is a healthy diet and exercise.