Can stress cause myoclonus and fasciulations / twitching all over my body?

Stress will worsen. The stress is not the cause, but could make the symptoms seem far worse. Real question involves why you are experiencing the problems you describe. Do you have an over-active thyroid gland, is there muscular irritability, are some of the movements consistent with seizure activity, or a spinal cord problem? In essence, get a full evaluation, as this is not emotional.