Although many people can detect, from how they feel, whether or not their sugars are below normal, that is not always a reliable test. The measures needed to reduce the risk of hypoglycemia are the same ones used for careful management of diabetes. They should have a daily regular program of exercise. They need to check blood sugars often. If there is any hint of something wrong, check the sugar.
Early detection means prompt action can be taken.
In extreme circumstances, that action might be a Glucagon injection.