Nikutai Ten'i

Kenichi and several of his friends stay after school to look at a new archaeological find, a bizarre looking mirror. Suddenly, the entire building is transported to an alternate dimension and a magic field surrounds it to prevent them from escaping. Also, their minds have switched to other people's bodies. The only way to switch bodies is when their sexual emotions are high. Kenichi must find a way to return everything back to normal until the dimension falls apart.
(Source: Anime News Network)