I stumbled across this before I understood the basics of Buddhist meditation. I was exerting my will to fixate on and manipulate the imagery, and I suppose it would put me into a hypnotic vs. meditative state. Sometimes I'd even fall off into sleep, even though that wasn't my intent.

If I work on the wormhole imagery hard enough, it feels like I become part of it, hence the sensation of travelling down into it. And yeah, it's a very interesting experience.