@Rob6 This is a great question and one that we get a lot!
Most companies include anti-microbial technology in and around the inflation area, so the small chance of mold developing is nearly eliminated. Some pads even come with pump bags, further decreasing the chance of mold because you need very few breaths to completely inflate your pad with a pump bag.
Also the chance of your pad freezing internally is very minimal since pads are often used inside tents that capture your body heat and have a nice cozy sleeping bag on top of them. But on that note, you will definitely notice how the air inside the pad condenses if there is a dramatic change in temperature, so it can feel like your pad is deflating. The best way to avoid that is to either inflate your pad when the temperature cools down (so right before bed, not in the middle of the day) or add air to your already inflated pad if you notice or anticipate dramatically cooler temperatures. Hope this helps!