God and worship

Why some sundays when I get to church and have worship time, do I fall in love with God and can't think of anything else I would rather be doing then loving my God, and other times, I would rather be......well i would rather be doing anything but worshiping god. Now I know thats harsh, but its true. I simply hate it. I wonder why my heart longs for god at times, and at other times I seem careless of him. He should be my best friend, and my best friend I care about all the time. Or my father for that matter. I care for him all the time, shouldn't my God be that way to? Don't get me wrong I love God all the time, but it just seems at differnt "levels" at times.