Night terrors? Growing pains? Nightmares? Help...

Just wondering if anybody may have experienced what we're experiencing or know anything about our problem.

Our 26 month old son wakes about once a week in a complete state, crying, kicking and inconsolable. We can't do anything for him, no touching, holding, singing etc. and anything we try upsets him further until he's so worked up that sometimes he throws up. It's almost like he's conscious but still asleep. He answers questions - drink? sore? etc. with a firm no. It usually goes on for about an hour until he's so exhaused he falls asleep.

It's been happening for about 3 months or so and tonight it's been a particularly long episode (and is still going with my dh trying to settle him).

Has anybody experience this or does anybody have any suggestions or advice on tips we could try?