My efficiency is very high during exam week. How do I keep this high efficiency at other times?
You probably can't.
Exam periods are high intensity last minute sprints, exhausting and taking a toll on the other aspects of your life. Personally, I barely spent time cooking or meeting friends. My time was spent on life support activities (eat and sleep), studying, and regretting not having managed my time better. I also remember being exhausted and not being able to do much intellectual work right after the exams were over.
You can pull this off for a short period of time, but you cannot keep this for long without being burned out. Plan ahead, spread your workload, and make sure you get enough rest and leisure to keep your brain rested and at peak efficiency.
I'd say you can not. And I will not only compare it to my own experiences during university time - but also as a sports athlete that did lots of competitions on international level.
Like a sportsman you define which races (exams) you find most important - or at least where you need to put in lots of work to succeed. You will notice that you can't always succeed in the same way for every race (exam) - you will be burned out a bit after a heavy exam the same you will be burned after a hard race. You need regeneration - everybody will notice this after heavy work is done. You need to step back and enjoy your success - but in any way you need to get some sleep, meet some friends, have fun.
You manage to be fit and powerful just on top of the hill - this is where your race and exams starts. If you will exercise to be fit before this day comes you can not hold it until the important day comes.
So just lean back and be sure you do what you have to do when it is the right time and enjoy life in the times where you can. (This is in my humble opinion the most important advice I can give you for your whole life) - there is nothing wrong with you!
-- When you do some races on international level you need to qualify in some other races way before the important race day comes. Yet, you have to do really good on those qualification races. But anyhow - any athlete will not have his 100% race condition on those days - he will exercise and plan to have them just at the race day. And if you ever did sports and trained a lot for races you mostly experienced how awesome you did during the race and you never imagined before that you could do that!
I agree with the previous answers: you cannot keep up your efficiency as high as during exam time. However, I think you yourself know that it is not humanly possible. I think what you really want to know is how you can maintain a decent pace of work during other times, so that you are not so overloaded during exams. I would advise my students to follow this plan when I was teaching:
At the beginning of the semester, list down all the work that you have to do for the semester, breaking each larger piece of work into smaller units that can be completed in 2-3 hours.
Calculate the study time that you think you can devote comfortably each week and set targets for yourself to complete a few units within each week. Keep some buffer time, just in case you cannot complete one or two tasks or something urgent comes up that takes away some of your study time.
You have to ensure that you complete the scheduled tasks within the week.
Begin and end your stud time by having a look at the list. Tick off tasks from the list as you complete them. This will give you a sense of satisfaction.
Reward yourself on the weekend if you have completed the task; punish yourself if you don't. For instance, you get to go to a movie if you complete the tasks, but you cannot go if you don't. Change the rewards each week for novelty.
Hopefully, you will be able to maintain a good pace if you diligently follow this plan.