L.G.
Same thing happened to me - my daughter was easy to put to bed and a great sleeper (early waker, but at least she slept through the night) and then all that ended. First, I now I have to stay in her room until she falls asleep - that's new - and she wakes in the night - midnight, 2 am or 4sh - and if we don't bring her in bed, then no one is getting any sleep. So, for the past few months (she's 22 months and this started around 17 months) we have done just that. I know it might be totally the wrong thing to do - but we all have to get some sleep. My biggest issue is that she is awake everyday by 5:30 and ready for breakfast. Someone told me the other day that their 22-month old sleeps until 7:30 everyday and I literally started crying right there on the playground : ) Good luck.