Sounds like a sleep regression. You just have to power through them. I have friends whose little ones didn't sleep all night until 5 or 6 years old. Some slept all night from 3 months. Mine was 18 months old when he started sleeping through. Even then, that all goes to pot when he gets a cough or cold or some kind of illness. I have him with me when he's not well. My thought process was "when I was little and sick, all I wanted was comfort from my mum....what's different now I'm the mother?".
Another thought to your original post, (and this is my opinion though), I would NEVER IGNORE my little ones cries from bedtime to 7am (or whenever is getting up time in your household). Children CANNOT self regulate their emotions until they are MUCH older (5+ years old). YOU are their emotions regulater. Day and night. There's been a lot of research on this. I've working childcare for nigh on 20 years now. Nursery staff tend to answer every cry. Those children whose parents does this, and has nursery staff who do this, seem to settle better and enjoy being at nursery if they are emotionally fulfilled.
Yes, it's hard, yes you feel like you're continuously answer every whinge, and it will never ever end.......... but if a child knows that if they feel alone/scared/cant sleep/have night terrors or nightmares/aren't feeling well in the middle of the night, etc etc and they KNOW, without a doubt, you're there for them, they will cope a hell of a lot better as you, their emotions regulater, will help them and soothe them back to sleep.
Sorry for the long post, but from a point of view of a parent, and a point of view as a nursery nurse for nearly 20 years, children's emotions need your support, not suppressing! Adults seem to expect babies/toddlers to cope with large emotions. Most adults don't cope with normal emotions - why should small children be expected to?