Christianity is included in the traditions that practice possession. *gasp* Ever heard of the Holy Rollers? The Holy Rollers are a group of Pentecostal Christians who at one point in time during the mass would literally roll down the aisles of the church to whip up the energy. They would do this to invoke God within them and speak in tongues. According to my Pentecostal friend this is no longer practiced, but they still practice possession. They call it getting the Holy Ghost.
I could talk about this subject in an arm chair magician sort of style, but that's not who I am. I come from a line in my tradition that does possession with the Gods. My first taste of possession was, in fact, something that falls into: "this generally does not happen category." I was working on an oil devoted to one of our deities. I had contacted Her before I actually started working on creating the oil to ask Her what she desired Her oil to be like. I listened and took notes and this process continued for a few days while I asked questions, listened and played with energetic resonances of the oil mixtures I was testing for this project. When it came time to actually blend things together and leave it steep for the proper time I could feel Her hover near and my crown chakra would spin and become very warm. At the Dark Moon when it came time to bless this oil and call Her to empower it something different happened. I could feel Her half slip into me like a hand filling a glove and all the things I had planned on saying and chanting went right out the window. I could hear a difference in my voice, I could feel my eyes and other facial features being held in a different manner. I felt VERY large as though I could just stretch out and touch the other side of the house if I wanted to. It took a few hours after the blessing for the effects of Her coming and going to fully dissipate and even my kids looked carefully at me as though they were wondering who else was in there with me. I have witnessed another practicing this sort of possession and watching it happen on the outside I can tell you that there is a marked change in the person hosting the Gods while they are present.
While popular media likes to spin things in a manner of the sensational, the truth is that what ever it is they are spinning probably has another side and face to the subject and possession is no different. Possession is both sacred and profane and it is up to you to determine which you wish to embrace.