Which of the following symptoms could indicate heroin use?

Sleepiness is indeed a significant symptom that could indicate heroin use. Heroin is an opioid, and one of its hallmark effects is sedation, leading users to experience decreased alertness and drowsiness. This sedative effect occurs because heroin acts on the brain's opioid receptors, which can result in a state of relaxation and lethargy.

In the context of other symptoms, while body overheating, profound euphoria, and aggressive behavior might be associated with various substances or conditions, they are not as directly linked to heroin use as sleepiness. Body overheating can be more characteristic of stimulants, while profound euphoria is more common with initial opioid use but can vary significantly depending on the individual and their prior experience with the drug. Aggressive behavior is typically more associated with stimulant drugs or certain mental health disorders rather than opioids like heroin, which generally tend to depress the central nervous system. Thus, the presence of sleepiness is a clear and notable signal that suggests heroin consumption.