What should I do if I spill something on the mat?

Please, do not worry; even if the water soaked the mat, there are more waterproof layers inside, and it will be safe to use when it completely dries out. 

After it dries out, turn the mat on but do not lie down on it. 

Leave it on high heat for a couple of hours to check if the mat works fine. Just be sure that it is completely air-dried before you try to turn it on.