An altered level of consciousness is any measure of arousal other than normal.  Level of consciousness (LOC) is a measurement of a person's arousability and responsiveness to stimuli from the environment. A mildly depressed level of consciousness or alertness may be classed as lethargy; someone in this state can be aroused with little difficulty.  People who are obtunded have a more depressed level of consciousness and cannot be fully aroused.  Those who are not able to be aroused from a sleep-like state are said to be stuporous.  Coma is the inability to make any purposeful response.   Scales such as the Glasgow coma scale have been designed to measure the level of stuporconsciousness.
An altered level of consciousness can result from a variety of factors, including alterations in the chemical environment of the brain (e.g. exposure to poisons or intoxicants), insufficient oxygen or blood flow in the brain, and excessive pressure within the skull.   Level of consciousness may decline abruptly or slowly, or it may increase and decrease intermittently. Prolonged unconsciousness is understood to be a sign of a medical emergency.  A deficit in the level of consciousness suggests that both of the cerebral hemispheres or the reticular activating system have been injured.  A decreased level of consciousness correlates to increased morbidity (disability) and mortality (death).  Thus it is a valuable measure of a patient's medical and neurological<unk> .   In fact, some sources consider level of consciousness to be one of the vital sign.<unk> :<unk>  is a collection of<unk>  with change in cognitive contain, vigilance, and attentiveness.
Cognition: Cognition is a cortical function in which knowledge is gained by ones reasoning, or without the need for conscious reasoning (instincts) and  perceptions.
Vigilance: Vigilance is a calibration of awakeness.  Vigilance is low in sleep and is higher person is awake.<unk>  content:Mental content is a capacity of a person to integrate past and present experiences to the stimuli to the external and internal world.
Attention: Attention is an ability to choose and concentrate a stimuli from all<unk>  content which is relevant to a given situation.
Altered mental status
Altered state of consciousness
Somnolence
Snatiation
Psychomotor agitation
Pallor
Sedation
Myoclonus