Study right before bedtime (and don't sabatogue by drinking alcohol between studying and sleeping)--I have seen lots of studies that show that is a practice which will help you excel on your tests:

https://news.nd.edu/news/learning-be...w-study-shows/

If you get really tired; take a nap--you can always set your alarm if the nap is in the middle of the day and take a "micronap". A micronap is when you set the alarm on your phone so you only sleep 15-20 minutes--anecdotely I have read about lots of CEOs, people who are working on projects day and night, etc. taking naps but only sleeping 3-6 hours a night.....

Also, do some of your studying in a calming place like on a porch overlooking a beautiful yard, under an umbrella at the beach, etc and maybe that will be calming.....