The sitting-up thing, as far as I can tell, is what they call #ConfusionalArousal. (https://en.wikipedia.org/wiki/Confusional_arousals) It might or might not be related to #explodingheadsyndrome - they're both considered #parasomnias but neither is all that well understood. Mostly they're considered harmless and best handled by de-stressing and trying to get more sleep. Maybe consuming more magnesium, too.