I've always heard the term "whirling dervish" and never understood it.
It turns out that "dervish" is a Muslim sect especially in Turkey and Iran/Iraq. It's a fanatical sect (of Islam? surprise), a branch of the Sufi Islam which seems to be a bit more peaceful than the others (not a reach). I don't know but it seems like the Sufis turn their devotion inwards instead of outwards, and focus on their own behavior instead of the behavior of the rest of us. That's respectable.
Sufis believe that their primary goal is purifying their hearts and souls of thoughts other than of Allah, so they take on all kinds of activities that they figure will help them do that. That's what this guy is really trying to do. The "whirling" aspect is similar; not all dervishes do it, but it involves swaying and chanting and slowly building up to a frenzy of prayer. This frenzy often builds up to whirling, thus the term.
I can think of similar activity in other religions. The yogic flyers of Transcendental Meditation bounce up and down until they really believe they are levitating. "Speaking in tongues" remains a concept of Christian fundamentalists in this country.