What is this excruciating pain in my knee?

Over the last three months, on several occasions, I have had this sharp short and very painful bouts of pain that I can not associate with any activity, injury, illness, or infection. This pain which feels like I’m being stabbed in the knee with a hot knife, only lasts for 3 to 5 seconds. It has occurred in any position, at any time of day or night. The exact location of the pain, when it happens, is where the doctor hits you with that little hammer to check your reflexes. But not on the surface, it’s behind that tendon and a little to the left, on my left knee only, just under the knee cap in the little pit space the tip of your finger falls into on the lower left side of the cap just behind the tendon. When the pain occurs, it comes on fast and strong without muscle spasms, cramps, neurological blocking or numbness. I can be sound asleep, and when it wakes me, I’ll fall out of bed withering and howling in pain. Then like someone flicks a light switch, the pain stops after 3 to 5 seconds of agony, and I’m perfectly fine. Stretching, jumping, twisting, and pounding on my leg makes no difference to it. Before and after these attacks, I am perfectly fine, and have no pain whatsoever. There is no palpitable inflammation, lump, node, or discoloration detected. I almost feel as if someone has a voodoo doll of me they stick with a pin in the knee when ever they feel like it. I have nothing to show my doctor, and can not make the pain happen for him. One time it happened while I was driving and almost made me crash. When it happens in public, I usually do this strange dance and howl in pain, which is very embarrassing. What the #%*! is it?