15 month old baby suddenly waking up at night, crying hysterically.?

She was so good with her naps and night time sleep, she would give me no trouble at all. She's been sleeping through the night for a couple of months already. But two nights ago, she suddenly started waking up and crying very loudly and hysterically. She would only calm down when I picked her up. Last night we even had to take her to our bed and that's when she finally fell asleep. She would act the same way during naps now too. Since she just recently had an ear infection I took her to the doctor today and she said her ears are fine and she may be teething or it may be night time terrors. I gave her Tylenol before bedtime and it didn't seem to work. I don't think it's night time terror because on the handout it said the baby cries but is in a dreaming state still. And she's clearly awake when she cries. Right now she's crying again. I've been going into her room to check on her regularly and everything is fine, her diaper is fresh and I don't know what to do. She calms down when I comfort her but as soon as I leave she'll start again. I just wonder what happened to her since she was such a good sleeper. Has this happened to anybody and what did you do about it? Is this just a phase? Like the doctor said, she is fine health wise. But what could be wrong then? I need responses now as she is crying and I don't know how to put her back to sleep.