Snoopy is correct that it is a sensory symptom, and it's "official" name is Paraesthesia:

"Paraesthesia describes a number of abnormal sensations just about anywhere in the body. These include tingling, prickling, pins and needles, electrical-type buzzing, burning, skin crawling, itching, partial numbness (like feeling through tent-cloth) and a variety of neuropathic pains."

http://www.mult-sclerosis.org/paraesthesia.html

http://www.mult-sclerosis.org/mssymptoms.html

So if you've ever had an abnormal sensation, this is 'just another one'. I have had them stand alone (i.e. not in an attack), or as one of the first indication of an attack coming on. That feeling you have described most often gets my foot, and it seems to only happen when I am driving (position?). I thought my car was leaking under the dash for a while, until I realized I wasn't actually wet.

Cherie