Hi,
I have just come back from a retreat conducted by Fr William Goh.
Well, I never fond of Charismatic movement, though I don't think
it's bad either. I went to this retreat without knowing what it's
all about haha...
Anyway, regarding the topic "Slain in Spirit", I really experienced
this myself. It was quite unbelieveable because there were about
120 people in this retreat. And probably as many as 90% of us are
all fall down or having other spiritual manifestation.
Oh...wait..actually I'm not really sure if I'm referring to the
same thing, cause some people say it as "rest in the spirit".
As for me, I also fell down, but I'm still fully conscious. I just
cannot resist it, when Father prayed over me, suddenly I felt my
leg became very light and immediately fell down. But I was still
fully conscious, I can hear the music, people singing, etc. I was
able to wake up not long after that, but after that tears ran down,
and there is a feeling of happiness and touched at the same time. I
must say, it's a great experience, and I thanked God immensely for
this exerience. 
But also, I don't think it's something that we have to be too
excited about. Because the great mystics like St Teresa or St John
of the Cross always remind us of the danger being too fond of this
spriritual manifestation. Nevertheless, we have to thank God, if He
come and give us this. 