My 6 month old daughter did the same thing. She was sleeping through the night since she was about 3 months old and then all of a sudden, she started waking up around 2am. I would feed her and rock her back to sleep (it would take about an hour), but I was getting really frustrated. I talked to my Pediatrician at her 6 month check-up and he said it was separation anxiety, which is common at that age. The baby doesn't understand that just because he can't see you, you are still there for him. I started putting her to bed at 8pm, which was an hour earlier than I had been putting her down. I figured the later I kept her up the longer she would sleep, but she was actually getting overly tired, which made it harder for her to sleep. The Pediatrician told me that in order to get her over the separation anxiety, I could check on her when she started crying in the middle of the night (to make sure she was not physically hurt), but that I shouldn't feed her. He said I could pick her up and let her know that I was still there for her and then put her back down. He said to leave the room for as long as I could stand it and try to let her cry herself to sleep. If I had to go back in there in 5 minutes to reassure her, I could, but he said to wait 10 minutes before I went in again and gradually make the time longer between going in again. This sounded cruel (for both me and her), but I tried it and after about a week, it worked. After a while, she learned to soothe herself back to sleep when she woke up in the middle of the night, knowing that I was still in the house to help her if she needed me. Check out some information on the internet ("Google" - baby night separation anxiety). There are tons of websites. Also, check with your Pediatrician to see what he recommends. Now she sleeps from 8pm - 6:30am or 7am. Good luck!