No sleep... so tired... ARGH!

Two weeks ago the Bug started waking up in the middle of the night crying. She needed comfort, and probably needed Tylenol, too - her top left molar was coming in. This passed after a few days, but re-started again after a few more. I think the top right was making itself felt.

The last four or five nights, though, have been terrible. For Joker and me. The Bug is waking up, crying out for us, whimpering, making a fuss, which escalates until she is hysterical and we need to calm her down. I'm not sure what happened (she's been a great sleeper for 15 months), and we don't know what to do. So every hour or two, both of us are awake and one of us is out of bed. Plus I'm a lousy sleeper who has trouble getting back to sleep each time. We are probably exacerbating the situation by calming her down each time, but if she's not asleep we aren't either, and we don't want her to be miserable!

Is this a phase? Will it pass on its own? Any pearls of wisdom to share??