Can dementia change over night without having an infection or stroke?

Get her admitted to thehospital (NOT for observation; ADMITTED!!!!)

There is something going on.

Did they do a urine culture (takes at least 24 hours) or just a "dipstick"?  

Very unlikely that a drastic change in dementia isn't caused by some other medical issue.

Three things can cause dementia symptoms to be drastically increased:
1) Reaction to a medication, including inadvertently stopping one abruptly, taking too much, side effects kicking in ...
2) An illness. UTIs are notorious in this regard, but any infection can cause this, as can a cough, constipation ... anything not right with the body.
3) Progression of the dementia pathology itself.

Best wished to you.

This is exactly what happened with our mom. We called 911, they took her to the hospital, they ran test and found nothing wrong. We brought her home and she couldn't talk or walk and she slept for 2 days. Very not normal of my mom. We were able to get her admitted on the 3rd day. Turned out she had a stroke.

Thank you all for your responses. Im new to this site and I have found all of the info very helpful. I took my mom to ER and they refuse to admit her after doing a series of tests, including CT scan and urine and bladder check for infection. They also checked her for pneumonia. She has top notch insurance or I would have thought that a reason to simply send her home. After about 4 days she seem to be doing a little better but not much. I suspect shes had mini strokes which they said are undetectable until later. Her doctor daid there is nothing that they can do. She having a lot of vertigo now which she wasn't having before. She is not on any medication only vitamins and minerals. We tried in the past putting her on the dementia meds but it gave her violent diarrhea. Has anyone experienced problems with vertigo/dizziness with their loved one? When the night time rolls around her personality drastically changes to frightened and scared.

Google "Sundowning". My mom was a totally different person in the early evenings; at first, my SIL and I each thought the other was crazy, lol.

Is there a geriatric psychiatrist or other doctor who is familiar with dementia who can listen to your description of what is going on? A seasoned practitioner will understand what is up and be able to prescribe the right meds to ease her in the evenings.

Do you know what type of dementia that she has?

I have seen progression occur in various ways. My LO, who has Vascular dementia, has had her stepped down progression occur pretty quickly. She went from walking with a care to a walker in a few days. Then, she went to a wheelchair in a few days. More recently, she stopped being able to sit up very well, within a couple of days. All things have been checked, like UTI (treated and cleared), brain scan, and medication adjustment, but, it persists. We are now wondering if she might also have Alzheimers. It's not uncommon to have both, but, it's my understanding that AD is more of a gradual change.