In clinical practice, hospital admission of patients with altered level of consciousness, sleepy or in a non-responsive state is extremely common. This clinical condition requires an effective investigation and early treatment. Performing a focused and objective evaluation is critical, with quality history taking and physical examination capable to locate the lesion and define conducts. Imaging and laboratory exams have played an increasingly important role in supporting clinical research. In this review, the main types of changes in consciousness are discussed as well as the essential points that should be evaluated in the clinical management of these patients.