Not sure if it fits the full picture but.... but could be Night Terrors or Nightmares.
They do come on around this age,my DD1 used to watch Dr Who with DH and shortly after she had restless nights,screaming out loud,did'nt want to sleep in her own bed etc.
Sometimes even watching something "normal" can trigger all this off,and its difficult at this age for them to tell you much.
With Night Terrors they wake up terrified but aren't aware that you are there,very difficult as a parent as you can't help,all you can do is "be a presence" make sure they don't injure themselves if they are rolling about,and wait for it to pass.
My friends DS started this,but what triggered it off was difficult to tell,but she felt it was "change of routine" as they went on holiday,and overtiredness.
Some people reckon if you have a realy regular pattern,you could break the cycle by waking them up slightly before they start,but that only helps if it is a regular time.
I think you need to "Rapid return" them to bed when they are calmer,stay with them ,and "ride the storm" as there are no easy answers if you can't identify a cause.These things usually come in phases,that they grow out of.......Not much help now though