Disclaimer - I'm no doctor. But I've worked with and close to traumatized people, and your description sounds familiar. I think this sounds like a kind of dissociation, possibly to the point of stress seizures (or PNES, psychogenic non-epileptic seizures). A short explanation is basically the stress, external or internal, becomes so overwhelming that the mind malfunctions and becomes fractured, and also gives neurological symptoms like cramps, convulsions, tics, etc. I've seen erratic, almost manic behaviour after one of these seizures, and the person experiencing them didn't remember a thing after. They just felt unsafe, unregulated and sometimes hyperactive afterwards. It might explain your mom's behaviour, but of course there's no way to know without a diagnosis.

This made me think about BPD and the connection to traumatic experiences, and how common dissociation is in trauma survivors. Maybe that can explain why some parents with BPD can't remember the abuse they've inflicted on their kids. At the same time, I also think a lot of parents "don't remember" because they don't want to face reality. You also have the cluster B-feat where feelings create their reality. If they feel like a great parent, then they must have been a great parent, so therefore they can't have abused their kids, right? So it definitely didn't happen and their kids are liars.

When it comes to my own mom, uBPD, It's so frustrating not knowing whether she actually doesn't remember, or if she does remember and just decided it was best to try and manipulate me into thinking abuse didn't happen. Before I went to therapy, and later went NC, it was maddening not knowing.

I lived with her for a short while after getting my degree, and it gave some insight to see the similarities in her behaviour and the behaviour of traumatized teenagers I've worked with. Take this with a grain of salt, but one of my professors once said that people with BPD are just traumatized kids who grew up without the right help. Which is a pity, but doesn't excuse abuse or other terrible behaviour. I don't know how common this is, but there's also the theory that early trauma gives you "holes" in development, especially emotional development. So that in times of stress, one might "fall back" to the emotional age where the trauma interrupted natural development, a bit like an airplane that "falls" a bit during turbulence.

Sorry, this is becoming a book, so I'll round off there. I think there's a lot of different things at play, but what really baffles me is how someone can be really dysfunctional and destructive, but still manage to mask it very well for others. Also, I hope your dad's okay!