FIGURE 1.

A two-dimensional representation of consciousness. The X axis represents the Content of Consciousness, the experience of which can vary in vividness. The Y axis represents the Level of Consciousness, or wakefulness, or vigilance, or arousal. Clinical conditions are in red, while normal physiological states are in yellow. Solid lines indicate transitions between states that require a change both of content and of level of consciousness. Conversely, dashed lines indicate transitions for which one dimension remains constant.