When I got tests or exams coming up I have to work (study) for like 16 hours a day. And when I don't have tests or exams I still have to study every day... And people who work for 8 hours still complain, students work way more than most people. Working from 10am to 6pm and not doing anything else for the rest of the day and the weekends is much easier than university students work.
The trick for not getting tired is to make physical exercise, I do it every day, and I go for a run every time I can.