Schizophrenia: This is often considered due to its prevalence among psychiatric conditions that can present with acute psychosis. However, the acute onset might also suggest other diagnoses.

Bipolar Disorder with Psychotic Features: Acute onset psychosis can be a manifestation of a manic or mixed episode in bipolar disorder.
Substance-Induced Psychosis: Various substances, including drugs and alcohol, can induce psychotic episodes, especially in individuals with a history of substance abuse.
Brief Psychotic Disorder: Characterized by a sudden onset of psychotic symptoms that last for more than a day but less than a month, often triggered by a stressful event.

Neurosyphilis: Although rare, it can cause psychiatric symptoms, including psychosis, and is crucial to diagnose due to its treatability.
Central Nervous System (CNS) Infections: Infections like meningitis or encephalitis can present with acute psychosis and require immediate medical attention.
CNS Tumors: Tumors in the brain can cause a variety of psychiatric symptoms, including psychosis, depending on their location.
Autoimmune Encephalitis: Conditions such as NMDA receptor encephalitis can present with acute psychosis and have a significant impact on prognosis if not treated promptly.
Thyroid Storm: Severe hyperthyroidism can lead to psychotic symptoms, among other systemic symptoms, and is a medical emergency.

Prion Diseases: Such as Creutzfeldt-Jakob disease, which can present with psychiatric symptoms, including psychosis, in its early stages.
Vitamin B12 Deficiency: Severe deficiency can lead to neurological and psychiatric symptoms, including psychosis.
Wilson's Disease: A genetic disorder that leads to copper accumulation in the body, which can cause psychiatric symptoms, including psychosis, especially in young individuals.
Porphyrias: A group of disorders that can result in acute neurological and psychiatric symptoms, including psychosis, during acute attacks.