Mental confusion is the term used to describe a patient who is unable to orient themselves by place, time and identity. It can manifest as not knowing where one is, what day it is, or even who one is. It is often combined with delirium. It can be caused by a number of disorders, most of which are related to drug or pharmaceutical use, sudden brain injury, or long-term chronic brain dysfunction. The symptom is not very specific and can be caused by anything from the easily treatable (e.g. dehydration) to conditions that are serious and can't be treated (e.g. schizophrenia).