As someone who has frequent surreal disturbing scary dreams I don't consider a dream a nightmare unless I wake up shivering/hyperventilating/sweating still feeling afraid or otherwise awful
For instance last night I had a dream my home was under seige by shapeshifters and fish people and giant monstrous bats and something else so impossible large it cast a massive shadow on my home as it flew over. And also it was dark and none of the light switches would turn on. But I woke up refreshed and well rested so I don't consider it a nightmare