My father has dementia, and is talking crazy. should i tell him he has alzheimer's & dementia. ?

Difficult question: Without knowing full situation. You can have open, frank conversations with him when he is lucid, but if he not clear in thought the mention of these issues may bring about further irrational behavior. I would recommend including counseling and a psychiatrist for your father for best results and appropriate path. Best wishes during what I am sure is a difficult time.

No: Get him to his physician. If he is disruptive, call for emergency help if you must. Don't argue or try to reason with him. Try to find a placement for him if he doesn't respond to medication. You have my sympathy.

Get an evaluation: Not sure what you mean by talking crazy, but sounds like you should call his doctor for advice. A geriatric psychiatrist or neurologist who specializes in this area may also be helpful. Support group for family and caregivers can also give you support and let you know what helped them help their loved ones.

Agitation & dementia: Dementia not only causes memory loss but can be accompanied by agitation, paranoia & sometimes even psychotic -like symptoms such as delusions. Your father's doctor can suggest treatment options ( including placement ). The alzheimer's assoc & other groups can guide families affected by this painful and progressive illness. Of course if the situation is dangerous get help asap. Good luck.