What happens in 'cold shock' during hypothermia?

Cold shock is a response that occurs immediately upon sudden immersion in cold water. It involves a rapid and involuntary reaction that can include gasping, hyperventilation, increased heart rate, and a spike in blood pressure. This physiological response is primarily due to the body’s attempt to acclimate to the extreme temperature change and manage the initial shock to the system. The reflexive gasping can lead to the intake of water if the individual is submerged, significantly increasing the risk of drowning.

The other options represent possible effects of hypothermia or are related to prolonged exposure to cold, but they do not accurately describe the immediate response known as "cold shock." For example, immediate loss of vision typically does not occur with cold shock, muscle cramping can happen later in hypothermia due to reduced blood flow and muscle fatigue, and while an increased heart rate is a component of the body's immediate response, it is more accurately encapsulated by the term "cold water immersion reaction." This reaction, as highlighted, characterizes the initial response when someone is suddenly exposed to cold water, making it the correct answer.