Sudden unresponsive patient with normal vital signs: What is going on?

Purpose of review To summarize the differential diagnosis and diagnostic approach of sudden unresponsiveness with normal vital signs in various settings, including the ICU. Recent findings Sudden unresponsiveness may be either transient or persistent, and may result from primary brain diseases or nonstructural systemic conditions. Life-threatening causes should always be discriminated from those more benign. Regional epidemiology, for example regarding intoxications, and evolving therapeutic management, for example for ischemic stroke, should always be taken into account for optimal opportunity for rapid diagnosis and best management. Summary Sudden unresponsiveness with normal vital signs should trigger immediate and focused diagnostic evaluation to find or exclude those conditions requiring urgent, and possibly life-saving, management.