My daughter has the same exact thing occurring to her. I have been surfing these boards and just ran into this. I always thought is was b/c of her teeth. My son never had this as a child so it was alarming to me. But when I sat back and tried to ration it - I just thought it may have been her teeth maybe bleeding @ the gums - and mixing with her saliva (sorry to be gross). It has stained her crib sheets, so I really do think it is/was blood. Does it leave a staining on the sheets - or where she was sleeping? The drip going down your daughters mouth - looked identical to my daughters - although it depended on how she was laying - I haven't seen it happen to her in about a month or so though. Keep updated if you find out what the cause is. My daughter is not on any medications.