The best way that I have found to describe the ego, is "thinking about the self in third person". It's all the ways that you imagine yourself and define yourself.

As opposed to the experience of life in first person perspective, which is what the actual self is.

Also, as someone who's had "ego death" experiences, it didn't feel like losing anything. Instead I realised that I was everything. "Tat Tvam Asi". My ego is the tiniest fraction of all that I truly was.

And you're right, this is where the main healings from mental illness come from. My ego death experience on LSD cured my eating disorder. I write about it in my article "Thinking About Myself in Third Person".