What Causes Numbness In Mouth And Lips?

Recently (probably for a month or so) at random times the inside of my mouth and lips will go numb. it is almost always on one side, usually on the right. The last time it happened (3 days ago) the numbness traveled down the inside of my throat and along the whole right side of my face. It almost feels like that side of my face is swollen, like after a dentist appointment where they used novocaine to numb it. It lasts for about a minute then stops... What could this be? Its pretty frightening when it happens. I over-think things and keep convincing myself that it could be a stroke or leading up to one...