Have you noticed that when you've had a bad run of sleepless nights and you are at the end of your tether the baby sleeps through only to go back to their old pattern after a few days. This happened to me through 3 children then it finally dawned, Junior was't necessarily sleeping through the night, I was just too exhausted to hear. (confirmed with spouse who hears baby, thinks I'm going to deal with it and goes back to sleep again) Once I figured this out it was tough love. Ignore for a couple of nights, thats it, never wakes up again. (Obviously don't do this if the child is sick/under the weather)