3-Dystonia
Muscles become rigid in Parkinson, but may also undergo spasms and something called dystonia. This is an involuntary contraction of the muscle that extends for a long time and leads to an unnatural position in the affected extremity. This is often experienced in the lower extremities, and patients feel their foot suddenly becomes difficult to move, start contracting, and feels very painful as it twists into an arching flexion. This torsion or inversion of the foot is often described as one of the worst sensations and commonly appears when the patient is worn down or very tired.