Actually a driver has a the right to refuse to drive due to medical issues which includes excessive fatigue and there is nothing dispatch can do about it and they can not punish you for refusing do to these conditions.. I will look up the law if I can find it and post it I do know it exists
did a search came up with 1989 law 27f3-113 which gives the driver the right to refuse dispatch if he feels that he is too impared to drive and feels that he is a danger to public