Just like anyone, he might be thirsty at night. If you're solely breastfeeding, your milk is his food AND drink. LOL, and I was given some great advice from my Doctor who has 4 kids of her own (I was a worrywart!): she said "For the first year or two, nothing is normal; as soon as you think you've got a pattern figured out, or you think you know what they want, bingo, they change. You just have to adapt with them because they are growing and developing really fast!".
I've gotten up to nurse my son at night (even as much as 4 or 5 times when he was going through a growth spurt!), and he is a happy, contented baby. Currently, his body has been satisfied throughout the night with his last nursing and a little cereal, so he's sleeping all the way through, but if he does wake up again in the future, I'll be there to provide his nutrition;)