This sounds like night terrors to me too. My son had some on and off,
in similar situations where he woke up shortly after going to bed or
was woken from sleep (say fell asleep on plane and had to leave plane
when we arrived). It was indeed very scary as he seemed to be very
upset, flailed around a lot and even yelled but didn't seem to
acknowledge us and our efforts to calm him down.

We thought it seemed to happen more on nights when he was overtired -
eg had a long day, no nap (at the time) etc. Basically we tried to
make sure he was going to bed on time, getting enough rest etc. and
then when it happened we tried to stay calm, make sure he didn't hurt
himself by flailing around too much and comfort him if he "woke" up.

Good luck!