Too many Ketones in the body can cause ketoacidosis, which is very dangerous.
First, to be completely clear, Ketosis is NOT diabetic ketoacidosis.
Ketoacidosis is a serious complication of uncontrolled diabetes that occurs when your body produces high levels of blood acids called ketones in conjunction with high levels of glucose. You can consider comparing therapeutic ketosis to ketoacidosis to be like comparing a fireplace to a house fire. Fire is a great and useful thing when controlled and in the proper situations, but it also has the potential to become very dangerous if not used properly. Ketones are extremely therapeutic and beneficial when in a certain blood level, but are very dangerous at extremely high levels. In therapeutic ketosis, total blood ketones are in the 0.5-5mM range while in ketoacidosis, blood ketones are typically > 20mM.
This is a huge difference. There is no cause to be afraid of elevating blood ketones to the levels seen in therapeutic ketosis, but rather this level of ketosis is associated with many health benefits (improvements in metabolic health, weight loss, neuroprotection, etc). Until very recently, the only way you could receive the many benefits of ketones would be consuming a calorie restricted or carbohydrate restricted ketogenic diet. This also means, though, theoretically, you can elevate your blood ketones to any level depending on how much of the product is consumed.