The commonest and simplest operational definition of consciousness is, the state of the patient’s awareness of self and environment and his responsiveness to external stimulation and inner need. Therefore, unconsciousness has the opposite meaning, that is, a state of unawareness of self and environment or a suspension of those mental activities by which people are made aware of themselves and their environment, coupled with a diminished responsiveness to environmental stimuli. Loss of consciousness can have many different causes, for example, stroke, traumatic brain injury, anesthesia, brainstem lesions and sleep, the various causes of unconsciousness primarily interfering with different brain functions. Clinically, impaired consciousness such as coma, vegetative state (VS) and minimally conscious state (MCS) is a very common manifestation in subjects with acquired brain injury. Unconsciousness does not always consist of a general suppression of the entire activity of the central nervous system. Depending on the actual cause(s), many functions, such as protective reflexes and various cognitive processes, can remain intact. The Management of such a patient in VS or MCS requires carefully reaching the correct diagnosis, pronouncing an evidence-based prognosis, and thoughtfully considering the medical, ethical, and legal elements of optimum treatment (Bernat, 2006).