Mental cloudiness, also called brain fog or cognitive dysfunction, is the feeling that the mind is sluggish and hazy. People experiencing mental cloudiness may feel disorganized, confused, or disoriented; lack mental clarity; and have trouble paying attention, remembering, and even speaking. Mental cloudiness can make it difficult to concentrate, make decisions, carry out everyday tasks, and even carry on a simple conversation. Mental cloudiness is a symptom that may be caused by health conditions including excessive daytime sleepiness (EDS) and attention deficit hyperactivity disorder (ADHD). Mental cloudiness may also be caused by medications side effects, including chemotherapy drugs (often called "chemo brain.")