“Keep watch and pray, so that you will not give in to temptation. For the Spirit is willing, but he body is weak.” (Mark 14:38)
Being tired is not a sin. Failing is not a sin. Trying your best is all that God expects, at the very least!
But sometimes he will ask a bit more of you. Sometimes you have to drive yourself to do the extra mile. You might still fail, but at least you tried. You have shown your true Spirit.