Here is what it all comes down to:

Use your inner dialog to say something in the mind. Now notice that the mind was "seen" by awareness as it said something with the inner dialog.

Self realization is the realization that you are the awareness and not the mind. You are not the human. The mind is conditioned. Everything it does is stimulus response. Everything.

If you can "see" it then it isn't you. You are the awareness that is perceiving the content of consciousness. Move your body slightly, notice the will and volition to move. If you are the awareness that saw the choice unfold in the mind then who chose to move? The conditioned mind unfolded according to its conditioning.

When this "self realization" hits the identification with awareness becomes dominant over the mind. The feeling and sensation that you are the mind fades away and for the most part the mind goes silent and becomes still. What remains is a stillness that is perceiving a human as the human goes about everyday life. The best way to describe it is the thought and sensation of "I" is no longer there. Instead the universe is experiencing itself via the senses of the body and the conditioning of a human unfolds.

That is what people describe as the experience of oneness.

To get to the point of answering your question, what does it feel like to be an insect? The exact same awareness that is perceiving what it is like to be you is also perceiving what it is like to be an insect. Notice all of the sensations, thoughts and other characteristics of the human experience. The same perceiving awareness, the sense of being, is there experiencing the unique conditioned characteristics of an insect.

It all comes down to the sense of being. The fact that awareness is aware that it is aware. Everything feels this, it's just that rocks don't have a memory to remember experiencing it. Rocks don't have vision or hearing or a thinking mind or memory, there is only a very basic "I am" that doesn't even remember the previous instant in time of "I am".