Since you have got multiple sclerosis and you are on treatment development of new neurological symptoms definitely warrants urgent consultation with your neurologist. However while having beta interferon there could be transient functional deterioration of already existing symptoms of the disease which can evolve after physical stress, heat, fever. It usually occurs in first 24 hours of treatment and initial few months. Can lead to worsening of spasticity. This is my gut feeling. Please consult your doctor. Thanks