I woke up with 96.6 degree body temperature. what's the lowest it should be before i worry? i know 98.6 is the 'norm'.

Not to worry: It is normal for the body's temperature to drop overnight. Many of the metabolic functions go into a baseline mode, so less energy is needed and thus less heat produced. Understand also that an oral temperature is influenced by many factors and may not accurately reflect the core temperature. Don't worry too much about a low oral reading if you are feeling ok otherwise.