Stupor is the lack of critical mental function and a level of consciousness, in which an affected person is almost entirely unresponsive and responds only to intense stimuli such as pain.

[1] Short periods of restricted responsivity can be achieved by intense stimulation (e.g. pain, bright light, loud noise, shock).

[citation needed] Stupor is associated with infectious diseases, complicated toxic states (e.g. heavy metals), severe hypothermia, mental illnesses (e.g. schizophrenia, major depressive disorder), epilepsy, vascular illnesses (e.g. hypertensive encephalopathy), acute stress reaction (shock), neoplasms (e.g. brain tumors), brain disorders (e.g. alzheimers, dementia, fatal insomnia), B12 deficiency, major trauma, alcohol poisoning, vitamin D excess, and other conditions.

[3] Lesions of the ascending reticular activation system on height of the pons and metencephalon have been shown to cause stupor.

Doctors may administer IV antibiotics or fluids to treat infections and nutritional deficits, or conduct an MRI to check for lesions on the brain.