There are 3 other replies, but I don't think any are really ELI5.

The answer needs a few parts:

> What exactly is keto?

Keto is short for ketosis, a change in how your body uses energy.

Your body uses building blocks for all kinds of things. Two of those building blocks are carbohydrates also called sugars, and hydrocarbons also called fats and oils. The body uses them for many purposes including using them to make energy. In chemistry the difference is fairly small, carbohydrates (sugars) contain Carbon, Hydrogen, and Oxygen, and hydrocarbons (fats/oils) contain Carbon and Hydrogen. The body is able to burn both of them for energy but it takes a slightly different chemical reaction.

Normally the body likes to use sugar (carbohydrates) found in food. If you don't eat enough carbohydrates, your body switches over to use fats and oils found in food. It takes several days of not eating carbohydrates before your body decides it needs to switch gears and get most of its energy from the fats and oils in food instead.

Normally when your body uses sugar it converts it into energy, water, and carbon dioxide.

When your body is in ketosis, the process of using fats and oils generates energy, water, and carbon dioxide, but the different chemical reaction also produces some acids called "ketones". That's where "keto" and "ketosis" get their names.

More on this in the third part.

> What is acidosis?

Acidosis is when there is too much acid in your blood.

There is an acid/base balance in your blood. Normally your blood has a pH of about 7.4. If your blood becomes too acidic it is called acidosis. If your blood becomes to basic it is called alkalosis. Acidosis is when your blood pH drops below about 7.35. Alkalosis is when your blood pH goes above 7.45.

Both acidosis and alkalosis are bad for your organs. If the blood is too acidic or too basic, your organs will start to fail and you will die.

> What is keto-acidosis?

It is acidosis (blood turning acidic) caused by ketosis (using fats and oils).

Burning fats and oils is a normal thing for your body, and it can usually handle it just fine. Normally your body can neutralize the acids and extract it into urine just fine. Sometimes, your body can't keep up. Diabetics are much more likely to both produce more ketones and also have more difficulty filtering them out.

If your body can't process the ketones out fast enough your blood becomes acidic.

When that happens, your body quickly shuts down. It depends on how acidic your blood becomes and how quickly it is shifting, but for many people ketoacidosis will kill in less than a day. The damage the acid does to your body can be reversed if caught quickly enough, but if doctors can't fix the acid-base balance in your blood quickly enough, you can get permanent damage in just a few hours, and then die.

> is it possible to unknowingly get into it..

Yes it is possible, but your body will feel really sick, really quickly. People feel super thirsty, start throwing up, have stomach pain, act confused, and smell weird like fruit. Usually people will recognize something is very wrong and will go to the hospital.

Since people with diabetes are more likely to experience it, it's good to learn the signs if you are around diabetics.

It is easily treated at the hospital if it is caught in time.