
Losing out on sleep and studying that extra hour doesn't really help. Now, what you want to do well in an exam is good memory of what you have learnt. To have good memory, you should sleep well, Sound sleep for about 6 hours at least for teenagers and 8 for 55+.
Sleeping well not only helps in consolidation of memory but also makes your body to work efficiently the following day. Your immune system too becomes stronger plus most of all, you'll look good! (That is what we want. Don't we?).
Added to this, We don't see dreams when in REM Sleep, So you can save yourself from tons of nightmares and rarely good dreams however marred by stress and anxiety.
Lastly, Who doesn't love sleep, So manage your time properly and do the thing you love: Sleep Well!