Oneness is what happens when through any of various means--meditation, chanting, drugs, even injury--the right half of your brain comes to dominate your thoughts and perceptions. The lady in this video got there by a massive stroke that shut down the left half of her brain, a bit more extreme a method than any of us would choose, but she describes what she experienced in terms that sound very much like the way people describe the oneness feeling when they get it in other ways. Things like this--the ecstatic religious experience, for instance, or the peaceful sense of unity people describe from meditation--come from inside us. That's not to denigrate it, simply to point out, as this lady does, that all of us have this inside us all the time, and there are a variety of ways to reach it. I've seen people at church services get into a similar transcendent state through a process that looks to me like a kind of auto-hypnosis, as a whole bunch of them say the rosary in perfect unison. It involves shutting down that constant chatter and analysis you get from the left side of your brain and letting the right side do its thing.
Jill Bolte Taylor's stroke of insight | Video on TED.com