Drooling while sleeping might seem harmless or even a little funny. Many people blame it on sleeping in the wrong position, being overly tired, or having a stuffy nose.

In most cases, that’s true—it’s a minor and temporary issue. However, if you find yourself waking up with a wet pillow night after night, and especially if you notice other unusual symptoms, it might be your body sending you an important warning.

In some cases, frequent nighttime drooling can be linked to serious medical conditions, including certain types of cancer. Here are three cancer-related illnesses you should know about.