Clouding of consciousness Clouding of consciousness , also known as brain fog or mental fog , is a global impairment in higher central nervous functioning. All aspects of cognitive functioning are affected. On mental status examination it is manifest by disorientation in time, place and person, memory difficulties caused by failure to register and recall, aphasia , and agnosia . Impaired perception functioning leads to illusions and hallucinations often in the visual sensory modality. This then causes agitation and distress and secondary delusions . The term 'confusion state' is sometimes used to mean clouding of consciousness but should be avoided if possible because it is ambiguous. Copyright Notice Adapted from Wikipedia. Text is available under the  Creative Commons Attribution-ShareAlike License 3.0 ; additional terms may apply.