Suggest Treatment For Pain Under The Knee Cap

It does not happen often at all, but once in a great while I am awoke in the middle of the night by very severe pain under my right knee cap. I cant move my leg at all without it bringing me to tears. It usually doesn't last but 30 min. or so. Last night was more than an hour. I can still feel it the next day, but no where near as bad. I have never had any kind of knee injury. My husband asked what he could do to help. Nothing......any movement what-so-ever hurts severly.