I know its the long holiday weekend but I wouldn't hesitate to give your Neuro a call, their answering service can get to him or who ever is on call for him for you. The sudden loss of sensation and feeling like you may not be able to control your bladder etc.. could be a red flag that something is going on that needs to be addressed ASAP.
I have had a very similar incidence that I ignored until I was having so much trouble walking I fell. and also became incontinent for about 48 hrs. My feeling in my groin area never has fully returned. I was started on IV solumedrol as soon as my Neuro heard about what was going on. And of course I got the standard lecture that it is stuff like this that needs to be brought to his attention right away, and not to worry about what time of the day it is or what day of the week it is.
This is what they are there for basically is what he was saying. Personally I think I was in denial and hoping against hope that it would magically go away by it self.
Please go ahead and give your Neuro a call just to be on the safe side. Rebif is supposed to slow down the progression of MS, unfortunately there can be relapses even when you're taking it.
Take care and let us know how you are doing