I am new to all this DID stuff myself, just learning about my parts so I don't know how much I can help you. but I think I can answer your question...yes, they can cause you to have a nervous breakdown. they can trigger cycles, they can drive you crazy and like you said, try to kill you. I know I had a part that was trying to off me and it drove me to a major breakdown. when I thought I was DID years ago, I was frantic trying to figure it all out and it threw me into a major mania and my t said I needed to be hospitalized. he knew how much that scared me so he and pdoc worked together to medicate me and I checked in with pdoc everyday to stay out of the hospital. so don't worry, I wont tell you to go there. I am just trying to make nice with my parts right now because I am resentful of them feelin like they hold my mental health in their hands, they are the keys to me getting better and I have no control over them and I resent that. so I get angry and lecture them and then t says I am being an abusive parent and scaring them and they will never cooperate that way. so I wish I could do more to help you. you can pm me if you need anybody to talk to. take care.