Final answer:
Dehydration occurs when the body loses more water than it takes in. This can result in various symptoms and can be a medical emergency if not treated promptly.
Step-by-step explanation:
Dehydration occurs when the loss of water from the body exceeds the intake, resulting in a negative water balance. It can happen due to various reasons such as excessive sweating, vomiting, diarrhea, or inadequate water consumption. When the body is dehydrated, the cells shrink and cannot function properly, leading to symptoms like thirst, dizziness, fatigue, and low blood pressure. Severe dehydration can be a medical emergency, requiring immediate rehydration.