I need him every second too! How about every millisecond? :)
I do think our bodies respond by habit so much of the time. So if you are use to short fast, I can definitely see why it gets harder later.
"The Lord sometimes asks us to do things that are not easy. I know He is calling me to fasting and prayer. I recently heard a testimony of a man that said when the Lord calls him to fast, he finds it easy, but when he tries to do it on his own he gets weak. I wish this were true for me, but I do not find it to be the case. Nevertheless, I know He will help me."
The Lord for sure asks us to do things that are not easy. All throughout the bible we see this. I know it from my own experience too. And I believe the harder it is for us, the more glory goes to Him.