Sentence:  Sometimes your body doesn't make as much <WSD>spit</WSD> as it needs. When you sleep, your salivary glands take a bit of a snooze too. You're still making <WSD>spit</WSD>, but not as much. This is why your mouth feels dry when you wake up. 
Meaning of the word marked with <WSD> tags:  Saliva, especially when expectorated.