Depression: This is often the most common cause of memory impairment and fatigue in the general population. Depression can significantly affect cognitive function, including memory, and is frequently accompanied by fatigue.

Anxiety Disorders: Similar to depression, anxiety can impair cognitive function, including memory, and is often associated with fatigue due to the constant state of heightened arousal.
Sleep Disorders: Conditions like insomnia, sleep apnea, or restless leg syndrome can lead to significant fatigue and may impair memory due to the lack of quality sleep.
Chronic Fatigue Syndrome (Myalgic Encephalomyelitis): Characterized by profound fatigue that is not improved by rest, this condition can also affect cognitive function, including memory.
Hypothyroidism: An underactive thyroid gland can cause both fatigue and cognitive impairments, including memory issues.

Alzheimer's Disease and Other Dementias: While less common than depression or anxiety, these conditions are critical to diagnose early due to their significant impact on the patient's quality of life and the potential for interventions to slow disease progression.
Subdural Hematoma or Other Intracranial Pathologies: In older adults or individuals with a history of trauma, these conditions can present with cognitive decline and fatigue and require urgent medical attention.
Infections (e.g., Neurosyphilis, HIV): Certain infections can affect the central nervous system, leading to cognitive impairments and fatigue, and it's crucial to identify and treat them promptly.
Vitamin B12 Deficiency: This deficiency can cause fatigue, cognitive difficulties, and even neurological problems if not addressed.

Mitochondrial Diseases: These are a group of disorders caused by dysfunctional mitochondria, affecting energy production within cells, which can lead to fatigue and cognitive impairments among other symptoms.
Wilson's Disease: A genetic disorder that leads to copper accumulation in the body, affecting the brain and liver, and can cause cognitive decline, fatigue, and psychiatric symptoms.
Creutzfeldt-Jakob Disease: A rare, degenerative, fatal brain disorder that can cause memory loss, fatigue, and other neurological symptoms.
Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, characterized by cognitive decline, fatigue, and seizures, which improves with corticosteroid treatment.