If late-night marking and early starts leave you in a permanent state of exhaustion, you will be reassured to know that it's now official - you can catch up on sleep.
Researchers have discovered it is possible to bank sleep during relaxed periods, and store it up for the times it is hard to come by.
US scientists studied two groups of volunteers. One was allowed extra sleep, while the others kept to their normal sleep patterns. After a week the volunteers were then allowed to sleep for just three hours a night for another week.
Researchers found those who had stored extra sleep performed better in a series of tasks that tested alertness and reaction times.