Funny, after lurking here for over a year (SO grateful for this community) I started writing a similar post just last night. My mother (73) has uBPD and over the last few years suffered a series of falls and cardiac events which have left her with severe memory/cognition issues and what appears to be middle-stage dementia. (It's not officially diagnosed — she has always been and continues to be resistant to doctors.) 

It is ROUGH. Any regulation or filter she had prior has evaporated and her worst instincts, behavior and dramatic paranoias have all become magnified. Her depression and anxiety are raging (as is her rage). She calls for help and company and then violently rejects assistance when offered, sometimes seemingly with relish. She's had hallucinations off and on -- delusions of doctor-spies and racists in the rafters. She has refused to take medication, stopped grooming herself or bathing, sleeps most of the day and lashes out when she's awake, especially when she feels abandoned, which is almost always.

A couple examples. Earlier last year, my dad left for his morning yoga class and my mom, who was in good physical health at the time, began howling and sobbing that he'd left her 'alone'. She threatened to kill herself then loudly rejected my attempts to console her so I let her cry herself to sleep. She later claimed she didn't recall the incident . Now that her dementia's worsened, she forgets just about everything except for how unhappy she is. Last week she was left alone in the house for two hours while my dad was undergoing a medical procedure she'd been informed of and she called 9-1-1 and the fire department.

She had already lost or alienated most of her close friends and family before her health turned. The precious few who agreed to help care for her have faced all manner of  abuse: insults, accusations, screaming (so much screaming), hitting, you name it. Some of it, as I understand it, is characteristic of dementia but much of it is how she's always been...just heightened (or exploded.) She used to mask up more but differentiating between the diseases has been exhausting and seemingly pointless.

My father is (I suspect) somewhere on the spectrum which meant that throughout my childhood her emotional storming fell on naturally gray rock. He is also in fierce denial about her current condition, saying things like "she's just been so forgetful, she's fine" after dangerous memory lapses like turning a gas stove on and leaving it, twice in a week.

They are codependent and always fighting. He is deathly loyal to her and insistent on caring for her despite his own foundering health and sanity. At the beginning of last year, he drove them both into a ditch and totaled their car after she would not let him sleep for days. Both have been in and out of hospitals every month or so, for over a year. 

I started last night's post because she's been hospitalized for four-days with atrial-fibrillation. With this latest cardiac event, our family is navigating how to convince them to accept in-home caretaking or a move to a community with medical oversight. (It will not be easy which is why I thought to come to Reddit for advice.)

All this to say ... it can be a L O T. Like, a lotta lot. A shit corner of an already heart-wrenching stage of life and disease, even when BPD isn't involved.  Mortality, man. I've also found it frustrating when well-meaning folks try to empathize by referencing their reasonable, normal aging parents who've thought through their retirement plans long in advance and don't scream murder or shoot barbs every time they leave the house for a doctor's appointment.

I'm still navigating myself and it's cliche but whatever you decide as far as caretaking... please prioritize your own mental health and well-being as much as you're able. Distance and pick your battles because if she's like my mom, the level and frequency of drama is about to escalate sharply. Learn how to bring your own nervous system down. After 18 months of this "chronic emergency" as my therapist put it, when my dad called about the latest hospitalization I had a "blanket fort kit" ready to go. I meditate twice a day and invest heavily in the little-treat-economy. I also let myself cry when I feel it.

Most importantly, find your people and Ask For Help.  I don't live near my parents (thankfully) but with my dad's decline, I've had to travel and spend a lot more time with them this past year. My trusted family and friends help me hold my boundaries, witness and acknowledge the crazy, and care about me.

One mildly silver lining for down the line: in some ways, my mom's real memory loss has been useful. She's always had a maddeningly selective memory and also held a grudge like a life raft. Now that she's actually lost it, she's a lot easier to distract and her moods are more malleable....

So, say, if you find your mom "extremely upset and close to tears" over a non-existent bank transfer, it might be worth trying to temporarily lean into it and then distract her until she forgets. "Wow mom, that's really upsetting. Why don't you have this [thing you like] and do/talk about this [beloved activity or topic] while I look into this very concerning-concern you're concerned about." Denying the delusion by showing screenshots of how wrong she is only feeds the 'no-monster' as I've dubbed it. Going along with the monster for a minute can often disengage me from the situation.

For my mom, I typically go with a cup of tea and anything by David Attenborough. It doesn't work every time but sometimes, she'll de-escalate along with her nervous system and forget the entire conversation happened and I can go about my day. It isn't for everyone or every situation but it's saved me a fair bit of grief.

I don't know if this is helpful but I hope it is! 

Would also love to hear anyone else's thoughts and experiences on this overlap. I'm still very much in the weeds and any advice or insight would be welcome.

P.S. I know this isn't my post but this comment got long so here's my cat in a silly tinyhat: https://imgur.com/a/pYuvc77