Brain fog is a condition in which an individual is overwhelmingly forgetful, confused, detached and experiences difficulty concentrating. The term fog is used to describe this condition because it is like a cloud is clouding the way for mental clarity.rain Fog Preventions. One of the most important ways to avoid brain fog is to have a healthy diet. The brain needs a lot of nutrients and vitamins to function well. Lack of nutrients also causes infections to easily form which then increase the chances of brain fog.