Is it underlying feelings that have never come out before. I've been reading a lot of your questions and answers and frequently see comments about how your parent can be mean to the person they are closest to. Well that is what I'm experiencing now. My mother went into the hospital 3 days ago for a fall, and she has been wicked to me. I know she doesn't feel well, but her whole demeanor has changed. Maybe it's the Oxycodon she's on. She also fired the night nurse last night and refused ortho this morning, The nurses look at me like they feel sorry for me having to deal with this and also trying to keep their patience with her too.
My father mellowed as he aged. Not that he was ever "mean" but he became less apt to make rude comments. He died of lung cancer. My mother simply did not have a mean molecule in her, so even with dementia she was sweet and pleasant and maintained a sense of humor. She died at age 94 of "natural causes." My husband's journey through dementia included some stages where he was difficult and "not himself." But mostly he remained the mild-mannered, polite, and happy guy he had always been.
But it certainly is true than many people get pretty crotchety as they age. brdlvr1, your mother is in a confusing place. She is in pain, and on pain meds. I wouldn't take her present behavior as a prediction of how she will be from now on. Be patient, and wait and see.
About those social filters and whether we are seeing the "real personality" as they fall away. People are not born knowing when to say please and thank you. We do not know from birth how to distinguish the times we should be candid from the times we should keep our opinions to ourselves. All of these "filters" are learned as we are growing up. I consider what I've learned along the way as "real" as any traits I've been born with. Don't you? And if those got stripped away, the more-infant-like person that shows up would not be the real me!
Filters do tend to fall away with age. But it takes dementia to really play havoc with them!