Create a schedule and pace yourself. Most of your time will be spent studying but breaks are needed.
Go for a walk or do your preferred exercise. Just remind yourself how much better one usually feels after a good workout. Helps to clear the mind and re-energize the body.
Eat properly. You will be better off eating balanced meals than relying on caffeine, sugar and nicotine (for those who smoke) to see you through exams. On the other hand, now is not the time to give up cigarettes if you do smoke. Give them up after exams.
Get a good nights rest before exams. Cramming will not do any good if you are so tired and the brain foggy.
OK, you already know all of this, but it doesn't hurt to be reminded.
Good luck with exams!
Ernster, the Virtual Library Cat
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