One of the most important topics for diving never taught or discussed is Spatial Disorientation and its effects. Spatial Disorientation isn't taught because most divers simply don't know about it. Yet Spatial D. as a subject has been around for over a hundred years... In aviation. Aviators the world over are taught and maintain currency on Spatial D. and its effects, and they know exactly how dangerous it can be. Spatial Disorientation applies equally and directly to diving. Learning about this subject could save your life one day, and this book is the start of introducing it to divers everywhere. This publication was written to address the lack of information that exists today regarding spatial disorientation and its effects as it relates to divers. Spatial disorientation contributes more to causing accidents than any other psychological problem in a multi-directional space, such as diving underwater or flying through the air. Regardless of their amount of time or experience underwater, all divers are subject to disorientation. The human body is structured to perceive changes in movement when standing vertically on land in relation to the surface of the earth. When diving, the human sensory systems-the visual system, vestibular system, and proprioceptive system-can and will give the brain erroneous orientation information due to positioning and movement of the body in a space and along an axis foreign to our biological design. This information can and will cause some degree of sensory illusions, which in-turn lead to spatial disorientation, that further leads to confusion, lost time in actions, potentially harmful or dangerous reactions, and a developing spiral of out-of-control events leading to an accident or death.