Low or high blood sugar: which is more dangerous?

Both low and high blood sugar can be dangerous, but low blood sugar is usually the more immediate threat, says diabetes specialist Dr Rajiv Kovil. Hypoglycaemia can progress within minutes from sweating and trembling to confusion, seizures or unconsciousness. The American Diabetes Association defines levels below 70 mg/dL as hypoglycaemia, and below 54 mg/dL as needing urgent attention.