Frustrated by the tales of fancy and falsehoods that constantly stream from my mother's lips. Any thoughts?

Ah, applesed1, I know your situation in many ways: the rational times of discussion when she appears lucid have been the koolaid my mother has served to everyone for years. It tricks you into misunderstanding and then having to do a reversal when she is so irrational at another time. It makes you question your own veracity, memory, and sanity. Only recently did my only brother realize and adopt what I call the 90% rule with me: if you're lucky, 10% of what she says has some foundation in truth; the rest is total BS that comes from some image stuck in her brain. (And that is because he stepped up to stay with and share care for her after she fell last year). The bad news is those who only spend short periods of time with her or don't know the truth chug that koolaid right down (including cousins, attorneys, guardians, et al.) and my mother is still often able to be "on" for those times. The good news is her genius at covering is starting to fall prey to her paranoia, memory loss, and lack of reason and those are thus now more apparent to others.
On many of the threads here I have found comfort in the notion that I am not the only one whose parent has told others what a slut, drunk, control freak, blah, blah, blah, I am over maybe 8-10 years. She's on the verge of accusing me of outright stealing. I now know it was the dementia coming on slowly…though hard to detect because much of this behavior has been there since I was a kid.
Captain's advice is sound: instead of arguing or trying to reason with someone who can no longer reason rationally, walk away, hide yourself in a room alone, do what it takes to protect your sanity and well-being and that of your family. Use any and all resources available. I am gradually losing the guilt as I move to get my mother into assisted living because professionals will be better able to handle all this without the emotional entanglements.
I am preaching to myself. I still don't always succeed either at avoiding shouting matches with someone who makes no sense when she snaps about bathing or whatever simple thing sets her off….
Please remember you are no good to anyone if your own health suffers as a result of this stress. Your wonderful husband and children probably haven't been called to sacrifice you in exchange for her. Do the best you can by her without losing your self, your life, your job, your family.
Though my mother has always thought differently, everything is not always about her. Sometimes it's about others and what is best for them.
Please vent here, know others share your pain without judgment. And when you can, remember to laugh. (The outrageous stories, repetition, and ludicrous behaviors have become my and my brother's material for many an outright guffaw!)
Hugs, prayers, best wishes. Press on.

Accept that your mother's reality is not our reality. As her condition progresses, you will see less and less of her. Seek professional support from a geriatric care mgr or health advocate with a geriatric work history to guide you through the maze. Many healthcare advocates will also help with lifestyle management- e.g. scheduling weekly housekeeping, in-home prepared hot meal for the family, arrange for a companion for your mother, etc.

Don't think you have to do it alone. There is support, if you know where to find it. With assistance and guidance, you can and will get through this.

it does drive you nuts trying to rationalize with jibberish. our more rational brains just bend under the load. finally in the last few months of my moms life i learned to walk away instead of talking in circles with her. that kind of understanding dont come easy. reading a lot on this site and online and attending an alz seminar a couple of times really helped me to see myself as the night watchman at a looney bin instead of an equitable domestic partner. the night watchman at a looney bin isnt there to correct or cure anyone, just keep them safe. near the end my mom even had days of paranoid schitzophrenia with visual hallucinations and i never tried to correct her. just tried to calm her and keep her safe.

Bless you, and glad you can vent here!!! It is hard and I don't live with my mom with dementia but the time we do have together is just like yours...paranoia, accusations, fantasy, I've heard it all...her imaginary cancer, imaginary hospitalizations, surgeries, doctor boyfriend, sexy wked trips with boyfriend (she's 90, no boyfriend), which has evolved to dead uncles visiting, you get the picture. It's painful.

I come to this place to hear from others and know I'm not alone and don't have it as bad as most.

I advise getting some outside help as much as you can, a housekeeper, caregiver a few hrs a week, whatever she or you can afford. You know she will get worse and that her needs have changed. No shame in realizing she may need more skilled care or more time than you and your family can continue to offer.

Can she attend an adult day program? Can she afford respite care for a couple weeks at AL or memory care center? Yep, it might cost $150/day but think of it as a vacation for you and your family...that could be a bargain.

Is she a veteran or spouse of veteran? You may need to get creative to find available financial resources to help out. Call or visit your local center on aging or senior center and speak with them regarding options.

No shame in wanting your life back and having had enough. We start out with good intentions but no one can be prepared for the realities of this aging thing, and we continue to work longer than our parents ever did, then spend our retirement managing our loved ones care.