I guess so. This is my first time hearing the term sonder, they seem like the same idea with different prose after a bit of reading definitions. Psychedelics are a shortcut to ego death, but they also distort the meaning a bit as you experience hallucinations at the same time so its overall a much more intense experience. Ego death is a well defined concept in buddhism, definitely not just psychedelics. Having said that, I would be 0% surprised to learn that the first Buddhist to have ever defined ego death did so shortly after a chemically induced trip to the stratosphere