I don't read parenting books. But I've traveled in enough mom circles to know about this phenomenon called the 4-month sleep regression. Something about how round-about 4 months old, babies leave their newborn deep-sleep patterns behind and enter a more adult-like sleep cycle of light sleep followed by deep sleep, REM, or whatever.
So, you nurse your little bub to sleep, or rock him to sleep, and lay him down thinking he's asleep, but really he's only barely asleep. And his little eyes flutter open and he looks around and he's like "WHOA, now where did that nipple go?!" And he cries. Because his world has essentially been turned upside down. In his mind, you might as well have swaddled him in a ratty blanket and left him out on the front stoop.
So, you try to assure him that you have not abandoned him. You pick him up and rock him or give him back the boob, and all is right again, and he drifts off... And then the whole vicious cycle repeats itself and you look at the clock and it's 5:30 am.
Miles doesn't read parenting books either. Or, if he does, he is an overachiever, because he launched headlong into the 4-month sleep regression about three weeks early. We're up just about every 2 hours at night. Sometimes more. Not only that, he's decided that naps are really no fun either. I try to tell him, "Look, see? Other babies sleep a couple hours during the day." And he just smiles and coos as if to say, "Mom, those other babies are weak."