Well, I've had nightmares that had scarier atmospheres than the one I'll elaborate on. One where my younger brother was possessed by a doll. One where our house was torn up by a tornado. One where I was in a haunted mansion. But this one that I had sticks out to me the most, because it has the clearest ending. This took place when I was younger. I was walking with my cousin and her mom in the wastelands. I look away for a while. And when I look back, they're gone. So I start sprinting around trying to find them. But I trip on a cliff and wall off. Right into sharp spiked rocks. And when I fall to the spikes, that's when I wake up. Not the scariest atmosphere, but it has arguably the scariest ending.