Do hallucinations and delusions begin abruptly?

On Jan 24, my mom, who has vascular dementia, left her home where she lived independently, to be treated for a persistent cough. She became agitated in the ER. They administered high levels of haldol and risperdal for 9 straight days, often concurrently ( up to 100 mg per day). She began on about Jan. 28 to have detailed hallucinations and explain complicated delusions. Although both medications are now halted, there is no change in her ideations. The Dr. says this is merely a manifestation of her disease. I have difficulty believing such detailed and extensive ideations began overnight. Tomorrow, my mother will be released to a locked door facility, the same woman who functioned quite independently three weeks ago.