It appears that a panoply of problems - from brain deficits to balance issues to metabolic problems to muscle issues - could interfere with walking in ME/CFS. Several portions of the process of walking - such as visually scoping out your path, planning the movement, moving your muscles smoothly, balancing properly, etc. could be effected. It's no wonder that for many people with ME/CFS a walk in the park is often anything but relaxing.
Walking and Thinking - Not a Good Combo in Chronic Fatigue Syndrome (ME/CFS)