Thank you to all the replies.
Just to answer some questions and clarify several things:
1. I sleep 8 hours a day, faithfully
2. I study 8 hours a day (in addition to attending lectures), faithfully
3. Why do I still need energy drink then? Three reasons.
First, The medical school I go to (will not mention the name for political reasons) is simply going nuts in terms of class competition. You just have to utilize all means to move upstream in the class rank. So if your peers stay up all night before the exam IN ADDITION TO studying everyday, you'd better do it.
Second, the amount of information, especially that which needs pure memorization, is overwhelming. Establishing long-term memory for such information is hard, therefore short-term memory (24 hours before exam) is extremely handy.
Last, it is unclear about what kind of role sleep plays in terms of knowledge condensation. Some says "sleep is knowledge incubation." Some says "sleep is knowledge dissipation." If I have to take a stance in this debate, I'd go with the latter argument. So pseudo-cramming* before the exam should be a good idea.
* "Pseudo-cramming" is a term invented by me to describe studying like mad before the exam in addition to studying regularly everyday.