In the winter when I turn down my thermostat at night and turn it back up in the morning, am I using too much energy to reheat the house? If so, should I continue doing this?

No matter how long you will be gone or asleep, you will save energy by turning down the thermostat. Heat escapes faster when there is a bigger difference between indoor and outdoor temperatures. When you turn down the thermostat, the indoor temperature is closer to the outdoor temperature, the furnace runs less, and you lose less heat and save energy. In the morning, the furnace will run a little longer to bring the house back to temperature; however, the nighttime energy savings is much greater than the energy needed to reheat the home.