Localized salivary gland infections are fairly common. If it gets red or hot or painful you'll need antibiotics, other than that it'll go back down on it own.
If you get it again, you may be having salivary duct stones, "sialoliths" - my mother gets them - they're annoying but not usually serious. They can be seen on x-ray. http://www.nlm.nih.gov/medlineplus/s...disorders.html
Tart candies, like lemon drops, can increase flow and reduce swelling.