Tibin
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2656292/
Dear
Tibin,
Thank you for posting this.

There's a lot of fancy science in that article, but the BIG idea is: you don't think or learn properly when you don't get enough sleep. Many many folks in the modern world skimp on sleep and then rely on caffeine or energy drinks --- those will make you
feel awake, but they don't do anything to repair the loss to cognitive abilities.
Brain researchers believe that a great deal of memory consolidation --- an essential piece of learning --- takes place in REM sleep, and the longest segment of REM sleep typically occurs in the final sleep cycle of the night. If one gets 7 hours instead of 8 hours, one typically misses this last sleep cycle with its mega-dose of REM sleep. This has a huge impact on the mind's ability to learn and story information, as well as the ability to think creatively and draw on intuition.
One of the best things one can do for one's overall GMAT preparation is to start the habit of getting 8 hours of sleep every single night. The modern electronically driven world makes that hard to do, but that habit is worth more than gold in terms of intellectual abilities as well as emotional and physical health.
Thanks again!
Mike