It happens to me too, if I stand too long without moving my legs. I will most definately fall, unless I can sit quickly. For instance, when I fell trying to get into my minivan, last Nov.. My weakness is on my left as well.

The lesson I learned was to always have a seat behind me and a place to hold on, just in case. and to do my strengthening PT & OT every day.

There really is no med for this? If it's your MS, then it's just a matter of staying as safe and as strong as you can.

Keep in mind that there are other more serious causes for this too, such as "Poor Circulation". See your Doc, to make certain.