Crying it out

Daisy has been sleeping through the night for the last two or three months, with only a little bump in the road here and there, but last night was possibly our hardest night with her ever. She woke up at 9:30 and wouldn't stop crying. We went in at intervals and soothed her back to sleep, but every time we put her back in the crib, she'd wake up and start screaming again. We weren't doing a very hard-core "cry it out," I don't think-- letting her go maybe 20 minutes at a time, then going in at soothing her. But at midnight or so, when Mark went in again to check on her (she'd been crying on and off for two and a half hours), he saw white foam at her mouth and a stain on her sheet, and then when he picked her up, she threw up her entire dinner. It was pretty terrible. We both felt like there had been something wrong with our approach, if this was the result. We had to change her and her sheet and clean her room (the vomit was everywhere). Poor Daisy.