What Are The Effects Of Being Addicted To Pain Killers?

Hi I have an aunt who is addicted to pain relivers and is and has been manipulating my grandmother for quite sometime now. she has became extream in her plights to manipulate her and now shes all of the sudden for no reason going into " complete muscle failure without a doctor telling her so I'm trying to get some information online about muscle failure but I can't find anything about it anywhere so is it even possable for complete mass muscle failure and if so what cause it and what are the symptoms etc