And when they had ordained them elders in every church, and had prayed with fasting, they commended them to the Lord, on whom they believed. 

Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward. 

And it came to pass, when I heard these words, that I sat down and wept, and mourned certain days, and fasted, and prayed before the God of heaven, 

So we fasted and besought our God for this: and he was intreated of us. 

Go, gather together all the Jews that are present in Shushan, and fast ye for me, and neither eat nor drink three days, night or day: I also and my maidens will fast likewise; and so will I go in unto the king, which is not according to the law: and if I perish, I perish.

Here, fasting ws done for three days. You would fast until God answered one way or another. You're going to get tired and your human nature will tell you that God has already answered. God's answers are never confusing. Also, make sure it is both food and water. God wants all. Anything less is not a total sacrifice. Fasting is meant to be uncomfortable. 

changed on Thursday, August 30, 2012 10:33:32 PM

Be afflicted, and mourn, and weep: let your laughter be turned to mourning, and your joy to heaviness.
Verse 10 - Humble yourselves in the sight of the Lord, and he shall lift you up. 

changed on Thursday, August 30, 2012 10:32:10 PM

Then said his servants unto him, What thing is this that thou hast done? thou didst fast and weep for the child, while it was alive; but when the child was dead, thou didst rise and eat bread.