We have this at my school, but instead it is "Failing to prepare, is preparing to fail".Failing to plan is planning to fail.
I know what your'e going through with the whole sleep deprivation and motivation thing and its tough. No-one is going to tell you otherwise or lie about that to you. But, like most of the people here are saying, the worst possible thing to do is freak. As hard as that sounds, that only serves to exacerbate the problem.
As for releasing the tension and being able to focus, just do whatever calms you down. Be it eating, calling a friend/s, pets etc Just do whatever will calm you.
On the other hand, if you are like me, I always try to psyche myself for study with music. Again, whatever works for you. There is one poem though, that I've always found that helps:
Our deepest fear is not
that we are inadequate.
Our deepest fear is that
we are powerful beyond measure.
It is our light, not our darkness
that most frightens us.
Your playing small
does not serve the world.
There is nothing enlightened
so that other people
won't feel insecure around you.
We were all meant to shine,
as children do.
It's not just in some of us,
it's in everyone.
And as we let our own light shine,
we unconsciously give other people
permission to do the same.
As we are liberated
from our own fear,
our presence automatically
I really hope that helps, and I hope you get through this ok.