Yes it is i have trouble with that i was just diagnosed in September.MS has so many symptoms doctors are still not sure what all they are .its weird but a few weeks ago half my face went numb and i wasnt able to feel or taste anything on that side ..just last week my legs was numb to where i couldnt feel them.so yes its a symptom.
I would suggest you contact your neurologist, if this is a completely new experience and has lasted over a 48 hour time frame, you are potentially experiencing another relapse with symptoms suggestive of spinal cord activity!
Keep in mind that not every thing is going to be primarily due to MS, you can still experience secondary or completely un-associated medical situations too. There is also the possibility of things like an additional structural spinal issue, slipped discs, sciatica, pinched nerves etc when it's bilaterally in your lower limbs, symmetrical, worsens with positioning like sitting etc.....it's generally a good idea to bringing the new issues to the attention of your treating neurologist so he/she can work out what is going on and what treatment options will help you the most.
Somethings can definitely be very scary experiences, it's not unusual to experience something for more than a few days though, longer periods are definitely more common with relapses so this not starting to get better yet doesn't necessarily have more meaning to it, it's still best to contact your neuro when experiencing mobility issues for a couple of days because of the chance it is a new relapse and IVSM is needed...
Let us know how you get on........JJ