An allusion to Lewis Carroll's Alice in Wonderland. To go "down the rabbit hole" is to enter a period of chaos or confusion. Can also be said when taking a hallucinogenic, as some suspect Carroll's novel was really about a drug trip.
School's starting up again, time to "Go Down the Rabbit Hole" once more.
To follow a thread or a lead that branches off from your initial objective, then (often) doing that repeatedly to get your self lost and/or completely off topic. This is based on the fact that Rabbit Holes (or "warrens") are often interconnected dens and tunnels with no apparent pattern to them, but in which one would surely get lost if followed impulsively. (See also: lost in a maze, or trapped in a labyrinth.) (This predates Lewis Carrol, whose meandering fantasies are very much like a random stream-of-consciousness exercise.)
I started researching Electric Cars, but started to Go Down the Rabbit Hole, following stories about Nikola Tesla, which eventually lead me to a list of David Bowie's movie roles.
To go down on a woman is to start her off with nice, long, passionate kisses on the lips, and then down to her neck, and then down to her breasts where you have your pleasure with them, and then you kiss your way across her tummy, and finally, you have ultimate pleasure with orally pleasing her pussy.