It is best to avoid using the infrared sauna right after eating a large meal or if you are particularly hungry. The reasons have to do with your body balancing heavy digestion with trying to control your temperature leading to discomfort in the sauna user. On a very empty stomach the body becomes vulnerable as calories are burned as the heart rate rises. It is best to simply think of this like going to the gym.
Drink water before you go into the sauna, perhaps bring some in with you. Hydration is important as you lose more water than you might realize through evaporation. Sports drinks and coconut water work very well for this purpose as well.
The reason for this is that as you sweat out toxins you will not want your wooden benches to absorb these.
While some people may believe that wearing more clothing in the sauna will cause you to sweat more, in fact the sweat will not evaporate and the body can become overheated quickly and also remain in contact with toxin-filled sweat which can get reabsorbed.
The sauna is meant to be a peaceful place, just enjoy your time and appreciate having a good sweat.