Hi there,
I don't know anyone with both NPD and bipolar. I do know someone close to me with diagnosed BPD, and someone else with undiagnosed NPD. Both have self-medicated with illicit/unprescribed substances, and I'm certain that the drugs exacerbated some of their more deleterious behaviors. There have been times when more "psychotic" episodes from them have coincided with heavier drug use. The "psychotic" behaviors seemed to go into "remission" when they were hospitalized and cut off from the drug source.
I'm just mentioning this because, though I'm no expert, I understood that bipolar typically emerges in early adulthood. That your SIL's bipolar behaviors emerged in her 40s seems unexpected. I'm not saying it's not true, I'm just wondering if something else is going on, or is a triggering condition, such as a reaction to medications.
Having said that, the pwNPD in my life can exhibit extremely aggressive behaviors. He has gotten into trouble with police for harassing-type behavior. There was one incident where the police held him for several hours, and he became increasingly agitated and aggressive, but they couldn't figure out why he was acting so weirdly--he wasn't just drunk or high. He made threats, but since he didn't actually follow through, the police couldn't book him. The police called around to try to get someone to take him in, but nobody would. They ended up taking him to the hospital, where he was treated for a few weeks. Let's just say this wasn't an isolated incident--the police have a file on him, and that's why they were able to call around to ask someone to take him. And the reason nobody would take him is that his NPD behavior is too much to handle. He is in a bad way, and I wouldn't be surprised if he doesn't live much longer, cutting his life short by 30-40 years. I don't know if he'll get in a fight, a car wreck, OD on drugs/alcohol or succumb to physical system failures (failing kidney, liver, heart attack, stroke?). It is very sad. But since he's NPD (in all likelihood), he thinks he's "special" and would never admit to having any sort of problem, whether a physical ailment, mental health issue or otherwise. Though he loves the attention he gets at the hospital, he doesn't follow doctors' orders and reverts to bad habits when discharged.



; and same for house projects, we make a plan when he is in a good mood, I follow what we had decided and he "can't remember" even making that plan. There are times when the kids will talk to him and he has no idea, its like he is there physically, but not there is no comprehension of what is being said to him. While he used to mention every once and a while small things about therapy, outside of saying he needs to leave at a certain hour because he has a group session, is all he has said for some time. I know that he had to have a mental health evaluation, but the results of that were never mentioned to me, and since I don't feel like that is my place, I haven't asked him. While I would like to be supportive, I feel like sharing his diagnosis would make him feel like a failure.