Final answer:
Peng is likely abusing hallucinogens, as his symptoms like increased heart rate, hallucinations, and changes in mood and memory align with the effects of these drugs.
Step-by-step explanation:
Peng's symptoms suggest that he may be most likely abusing a substance that falls into the category of hallucinogens. These symptoms, such as an increased heart rate, sweating, visual hallucinations, and mood disturbances, align with the effects of hallucinogenic drugs. Hallucinogens can cause users to see or hear things that are not present, induce rapid mood swings, and affect heart rate and appetite. Additionally, they can lead to psychological effects like depression and memory loss over time.