Final answer:
The described symptoms point to acute alcohol withdrawal, which typically begin within 48 to 96 hours after the last drink. The closest time frame provided in the question is 48 hours.
Step-by-step explanation:
The symptoms described in the student's question, such as confusion, fluctuations in consciousness, and tactile hallucinations (feeling of ants crawling on him), suggest the onset of acute alcohol withdrawal symptoms, otherwise known as delirium tremens. These symptoms typically emerge within 48 to 96 hours after the last drink in those with a history of chronic alcohol use and can last for a few days. Considering this timeline, the closest answer to the given options is (d) 48 hours since the last drink.