20 month sleep regression?

My daughter has never been a great sleeper, but not terrible either. The past week she has been a little more restless but nothing wildly unordinary.

Last night we had a first. She woke up at 10:30, screaming hysterically, hyperventilating and full tandtrum for 2 hours. Went back to bed around 12:30, only to wake up again with the same screaming and crying fit at 4am-5:30.

This was full blown inconsolable crying and screaming. She has never in her life done this. She is not a crier and during the day she is the happiest thing in the world.

She got her bottom 2nd row molars in. We think its the top molars coming in which are supposed to be much more painful than the bottom.

Anyone have anything similar? Molars? Night terrors or general sleep regression?