> an unusual ... definition

I don't think it's that unusual. It seems to me just to be a narrower version of panpsychism:

https://en.wikipedia.org/wiki/Panpsychism

Someone that has recently dies has pretty much the same biology as when they were alive. The conciseness is the main difference, I would say.

It may be helpful here to think about, at what point does a sense of self, of varying degrees, become evolutionarily advantageous?

An animal that doesn't have some kind of pair bond or social arrangement, and doesn't raise its young, has a lot less need for some of this emotional hardware than we do.

Whereas K-selected species that raise their kids have broadly the same need for it as humans.

That doesn't categorically mean it evolved with the first pair-bonding K-reproducer, or that birds have parallel-evolved emotional hardware like ours, but there's plenty of behavioural evidence there - the last common ancestor of birds and humans was small-brained and primitive, but investing in individual children probably evolved around the time of amniote eggs, just because they were so much more biologically expensive to produce than amphibian or fish eggs.

Is someone tripped out on mushrooms experience ego death and total disruption of sense of self still conscious? They may even contend they are more conscious than normal life, what with all the communing with the universe and whatnot.

Trees react to the world around them in many ways.