Cognitive dysfunction (or brain fog) is defined as unusually poor mental function, associated with confusion, forgetfulness and difficulty concentrating. A number of medical or psychiatric conditions and treatments can cause such symptoms, including Heavy metal poisoning (in particular mercury poisoning), menopause and sleep disorders (including disrupted sleep). The term brain fog is not commonly used to describe people with dementia or other conditions that are known to cause confusion and memory problems,[citation needed] but it can be used as a synonym for sleep inertia or grogginess upon being awakened from deep sleep.

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