Feeling exhausted? What should we do?

Isaiah 40:28-31

English Standard Version (ESV)
I am in the middle of an assignment and I feel like going on a roller coaster. At times, I am thinking that I' have got it right, everything clicks together, then an hour later, I feel rock bottom, confused.com! Maybe it's getting late too. I found this really encouraging passage, I'd read it before but as they say, you may hear it umpteen times before you realise that it is just what you needed to know. Help is at hand when you call on the powerful name of our Saviour Jesus-Christ! :) 
28 Have you not known? Have you not heard?
The Lord is the everlasting God,
    the Creator of the ends of the earth.
He does not faint or grow weary;
    his understanding is unsearchable.
29 He gives power to the faint,
    and to him who has no might he increases strength.
30 Even youths shall faint and be weary,
    and young men shall fall exhausted;
31 but they who wait for the Lord shall renew their strength;
    they shall mount up with wings like eagles;
they shall run and not be weary;
    they shall walk and not faint.