Jam – My ideas revolve around diet and insulin, of course.
In those mornings when you are feeling at your best, are you eating breakfast, especially carbohydrates or sugary cereals? When "fasting" overnight, the production of insulin is reduced.
Does your difficulty walking occurred before or after eating lunch? Can you keep a diary of what you eat and identify a connection between your symptoms and your diet?
My hypothesis: excess insulin (hyperinsulinemia) plays a major role in MS, as developed in my initial post: http://www.thisisms.com/forum/general-discussion-f1/topic1878.html "Insulin – Could This Be the Key?"