You will weep tears of joy the first night you get some sleep. And the second night you get sleep, you will thank God. And the third night, you will start to think that you imagined how mind-numbing the first three weeks of sleepless nights actually were. Then, the fourth night you will have become USED to four hours of continuous sleep which is just damn GREEDY and your baby will fix that for you by refusing to sleep again.
And then the next night you will weep tears of joy... and so on. I think this vicious cycle lasts until your child is seventeen, but I'm not totally sure.