In post-op delirium, a low dose benzodiazepine (such as lorazepam) or a low dose anti-psychotic (such as haloperidol) may be given. Some experts use no psychotropic drugs at all. The main aim is to find out what caused delirium. It could be due to a long list of causes: electrolyte imbalance, infections, endocrine problems, respiratory or cardiovascular problems, neurological problems like stroke. I am a geriatric psychiatrist and I have seen patients who were not earlier diagnosed with Alzheimer s disease land in delirium after surgery with general anesthesia. On careful questioning, family members often admit that the patient was not as sharp intellectually in the past year or so as he was all his life. There is usually history of forgetfulness for recent events, repeated conversations, repeated questioning, misplacing things, at time confusion, difficulty with reading, getting lost in familiar surroundings, not recognizing familiar people or often not remembering names of relatives/friends etc. You should ask your relation s family members such things. You may consult a psychiatrist who is trained to find out history of dementia. Hope this answers your question.