Sudden Dementia

So, what would it cause and how would it be detected / tested by a patient in a hospital?

It looks like a cat or skarn MRI of the brain is in order. It could be many different things. Just go to the doctor please.

Most anything that is not likely in the brain. CT or MRI can identify brain abnormalities. In addition there may be some type of hormone that imblance could be detected by blood tests. An overdose of medication can cause this type of problem.

more medication can cause effects similar to dementia ....

A blood test may be useful, should see a doctor thyroid could be deranged.