Holi - have you tried a new bedtime routine at all? We had dreadful problems with our daughter waking screaming in the night after being an amazing sleeper. She was almost 2 though, so slightly older than your LO. We got a new bedtime story (Guess How Much I Love You) and read her it every single night before bed. When she woke in the night, we would kind of do the end of the bedtime routine again, so instead of just cuddles, dummy and mobile, we would also read the story to calm her down. It did require some perseverance over a fortnight or so, but she eventually got back into her old routine of sleeping through. Also, if you have room, we found that rather than taking her into our bed, one of us sleeping next to her on the floor of her room was enough to settle her down. We left it as a last resort, but it gave her comfort without changing where she slept.