I am a scientist by nature, and I don't believe at all in God or any form of spirituality or the Holy Spirit (of course).

However, it does confuse me as to how some people genuinely do seem to be overcome by 'spirit' in certain more extreme churches.

http://www.youtube.com/watch?v=BuOBdGeArZw Watch this clip, and at about 3:35 the man goes into a strange state, and states like this do happen. As well as this, my dad once began crying for no reason in a Church or Mosque or something at the altar.

Are there any scientifically/theoretical psychological explanations as to why this could be possible without the need for any sort of spirituality?