When you do not know whether the sugar is low or high, a little sugar will help if it is low and will do no harm if it is high. Insulin would lower low sugar even further, and rest will not help, because your friend needs help right away.
Give your friend sugar or a sweet drink immediately. If their blood sugar level is dangerously low (hypoglycemia), this will quickly improve their condition; if it is high, a little extra sugar will cause no immediate harm, whereas a sharp drop in sugar can lead to a fatal coma.
Option 2. Rest will not correct a possibly low blood sugar level, which can quickly lead to a critical condition.
Option 3. Injecting insulin without knowing the blood sugar level can be fatal if the sugar level is already low.