User blog comment:Acebatonfan/The "D-word"/@comment-4364807-20140311040258/@comment-4196050-20140312195124

Low blood glucose is dangerous in the short term. For example, if I were to go low during an exam, I need to stop taking the exam and correct the glucose ASAP. Even something as short as 15 minutes can send me dropping into very unsafe levels (I believe seizures and unconciousness can occur with levels below 55. The lowest I have been was 45). Especially for diabetics who have been under very tight control, when low blood glucoses occur often, the symptoms become less noticable (hypoglycemia unawareness). When I was at my lowest, all that happened was that I woke up at around midnight, felt extremely lethargic and tired, and was confused as to why I woke up. It took a solid five minutes for me to go and check my glucose, and, by then, I was at 45 and feeling absolutely nothing.

Really high blood glucose is dangerous in the long term, because it increases the risks of complications. DKA is also possible with high blood glucose, and that can become immediately life-threatening if action is not taken within 24 hours after noticing symptoms/large amounts of ketones.