This pertains to more than just hot tubs but it is getting to that time of year when a hot tub feels really good. Your internal body temperature is a steady 98.6 f, 37 C. When your core temperature begins to raise it sets of a cascade of events that may cause erratic changes in your blood glucose levels. Some will see a rapid rise; there are a few individuals that see a drop. This phenomenon occurs due to an adrenalin release; your body is trying to reduce your core temperature. When you get an adrenalin release your insulin resistance goes up, your liver will secrete glucose, your heart rate climbs, and your blood vessel contract raising your blood pressure. This is in effort to get more blood to the surface of your body; blood near the surface can be cooled by the atmosphere and then recirculated back to your core. Problem arises that the atmosphere temperature is also high (hot tub) so your body responds by sending out more adrenalin. If you are going to use a hot tub or be outside just being aware of your body's signals, rapid heartbeat, sweating profusely, feeling ill, all will help maintain control of your blood glucose levels.