I know what you mean by something pleasant being scary in a way... one time, I was on LSD and 2C-B, and hit one charger of nitrous, and it was so different from normal; nitrous, instead of a rush of godly thoughts I couldn't grasp onto, I started immediately feeling the most intense physical pleasure I ever have, it was like a constant orgasm except even stronger than that, waves rolling out thro8ugh the tips of my fingers, all I could do was gasp and stare. It kept going and going too, for like 5 minutes, I was feeling so much pleasure that I couldn't think. And it was so different from other nitrous experiences. it started to scare me because it felt kind of wrong, in the sense that it shouldn't be happening. I didn't hit any more nitrous that night even though it was so insanely pleasurable.