Some Diabetics can have a loss of sensation in their feet, so don't use yours to check the temperature of water you're planning on getting into! You could cause major damage by stepping into extremely hot water and scalding or burning your skin, so use your elbow to test instead.
If you find yourself yawning more frequently than usual at a time of day in which you are ordinarily high-energy, low blood glucose levels may be the culprit. Take your blood sugar measurements to confirm whether or not this is the case; over time you should be able to identify your body's standard responses to changes in glucose levels.