About 8 years ago I watched a possibly made for dvd movie about a boys boarding school where they all became possessed and there were really overly long scenes of them in bed rubbing themselves. It may have been a religious school, and some new devil incarnate female teacher may have done rituals to cause the possession. There wasn’t much plot just people in bed rubbing themselves.
Voodoo Academy (2000)
http://www.imdb.com/title/tt0232908/
They ultimately get turned into voodoo dolls.