My DD has always been a fantastic sleeper. She goes for a nap or down for the night without objection and sleeps until she's woken apart - until two days ago. She does have a cold but last night and tonight has had a full-blown tantrum at bedtime. Last night she ended up in bed with me having cried on and off until almost midnight. Tonight I'm determined to leave her but she's been screaming for an hour and shows no signs of stopping. Help!!!