Is there a psychological explanation for people being 'overcome by the Holy Spirit'? 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?
Research in this area is pretty patchy. Summarizing what Wikipedia says on the topic:


"God helmet" experiments were plagued by failures to reproduce by independent research groups
TLE (temporal lobe epilepsy) and its effect known as Geschwind syndrome is one plausible cause... but that does not explain it in all people
hippocampal atrophy is a more recent hypothesis, although it seems backed by only one study insofar


Independently of Wikipedia I found:


a study by Urgesi et at. (2010) on the effect of brain lesions (following brain cancer removal) on self-transcendence, which determined that "self-transcendence increases after damage to lt and rt inferior parietal cortex". 
a 2009 study by Inzlicht et al. found that "religious conviction is marked by reduced reactivity in the
anterior cingulate cortex (ACC), a cortical system that is
involved in the experience of anxiety and is important for
self-regulation [...] These correlations remained strong even after we controlled for personality and cognitive ability." And the paper goes as far as having a "xanax of the people" heading for one its sections, and obvious pun on the better known phrase of Marx. The authors also point out that a similar anxiolytic effect was observed in studies of other strong beliefs, but not necessarily religious, e.g. ideological/political, citing Amodio et al. 2007 and Kay et al. 2008. (And starting to digress here, but the Amodio study has elicited strong reactions in the press).