15 month old DD has been crying hysterically every time I put her down in her cot. She stops when I pick her up but starts again and clings to me when I try to put her down. We have been doing this since 7pm tonight and she is still going. Doesnt seem to let up at all, just gets more and more worked up. She as been going for 10 mins now & I know she is stood up at the end of her cot. What do I do?