Which symptom suggests a severe state of intoxication in a substance user?

An unsteady gait is a symptom that suggests a severe state of intoxication because it indicates significant impairment in motor coordination and balance, which are crucial for safe movements. This type of physical instability often arises from the effect of substances, particularly depressants like alcohol or sedatives, which impact the central nervous system and can lead to decreased control over physical functions.

In contrast, a slowed heart rate can occur with certain substances but does not exclusively indicate severe intoxication, and may vary depending on the type of substance taken. Enhanced motor skills are not characteristic of intoxication; in fact, intoxication typically results in diminished motor function. Increased sociability can also be a result of some substances but does not necessarily reflect a severe state of intoxication, as it could manifest at lower levels of substance use. Therefore, an unsteady gait is a clear and reliable indicator of significant impairment associated with severe intoxication.