Which of the following is a severe symptom of poisoning?

Unconsciousness is a severe symptom of poisoning because it indicates a critical level of impairment in the body's normal functioning, specifically relating to the central nervous system. This loss of consciousness can be a result of various toxins disrupting the brain's ability to function properly, which can lead to inadequate oxygen supply, failure to respond to stimuli, or cessation of vital bodily functions.

Recognizing unconsciousness as a severe symptom is crucial in medical scenarios, as it often requires immediate intervention or emergency care to prevent further health deterioration or fatality. It emphasizes the urgency of addressing the poisoning situation, highlighting the potential life-threatening nature of the condition. Other symptoms such as nausea, dizziness, or excessive sweating can be concerning but do not typically reflect the same immediate level of danger as loss of consciousness.