Sometimes there really was ( or perhaps still is ) actuall rolling around on the floor.
I have watched a few of the tent meetings when I was a teen. My boyfriend and I sat in the back, watching out of curiosity to see what went on..and sometimes people would stand up wave their arms over their head and cry out..others would literally run around the inside of the tent and holler things like halleluyah or praise the Lord or come and get me Jesus ..and then still others would fall on their backs and have their legs go up into the air as if they're kicking and wave their arms and speak in gibberish or shout out praises or pleas to Jesus..or tell Lucifer to get back cause the power of Jesus was on them and they couldn't have them any more..things like that.
The first time I saw such a spectacle I know my jaw dropped wide open.. because my boyfriend told me that I might want to lift that jaw and close my mouth..I looked a spectacle like that, too.
I will never forget one black woman in a bright red dress..running up and down the aisle and around the inside AND the outside of the tent..she grabbed for me and my boyfriend and we jerked back..she wanted us to come running with her..and then finally when she looked as if she was so exhausted she'd drop..that's what she did..drop to the floor and moan and cry out for the entire rest of the service.
There were black people and white people in attendance.. and the service was being conducted by a white preacher who had an organist and a guy with a fiddle to assist him.
When we told some of our high school friends about it the next school day, the story sounded so outrageous a couple of our friends thought we'd exaggerated or made it up. Well the same preacher was still set up on the same highway going out of town the next weekend so we talked two other couples into going with us so they could see for themselves and before we all had to leave because we could not restrain our laughter any longer, they saw that we had not exaggerated one bit.
Each group I've ever seen like this were of a Pentecostal denomination..some would speak in "tongues" others were very similar to the manner of the Voodoo practitioners who believe they are "ridden" by the "Orishas" but with the Pentecostals, they believe it's the "Holy Spirit" being manifest in their life. They've had different names for their groups, often they speak of "full Gospel" or Apostolic or other forms of evangelical protestant belief.
edit: I live in Arkansas, and while I don't claim to know the name of every mountain, I can't help but wonder if the "uncle" didn't mean to type Ozark Mountains, rather than Oark Mountain? There are three main mountain ranges in Arkansas, the Ozark Mountain range, the Ouachita Mountain range and a Boston Mountain range, each with many different mountains in it. I'm unfamiliar with any Oark Mountain, but that doesn't mean it doesn't exist, I just can't locate it on my map.