your daily walking example is an inspiration.
I haven't had the symptom you describe but a good MS-friend of mine has had it and she has fallen over with it, and sometimes just comes to a stop for a few seconds. She's had MS 15 years, takes no meds, and this symptom disappeared fairly rapidly for her. I hope it disappears quickly for you too. My friend thought it was a relapse because it only happened her on a few occasions.
RR-MS dx 1998 and Coeliac dx 2003
Copaxone, Cymbalta. EPO, Fish Oils, Vitamin D3 2000 IU daily, Cal/Mag/Zinc, Multivitamin/mineral, Co-Enzyme Q10, Probiotics, Milk Thistle.