There is something called neurocardiogenic syncope. It is a conditon of positional heart irregularity. It can happen with MS but it is fairly rare. It is completely possible that your friend's fainting is from another condition. Unfortunately, having MS does not keep us from having other health issues. I hope your friend gets this taken care of and is feeling better very soon.
Here is a link on neurocardiogenic syncope.
http://www.hrtcare.com/neurosyn.asp