Sideways spinning is the first step in Akha spindle spinning. You can also use this technique with regular top whorl spindles. It's a great alternative to give your hand a break, or if your fibers are very slippery and you are putting too much "drop" in your drop spindling...
An Akha spindle is a "support" spindle in that you hold the spindle horizontally, twirl it with your right hand, and pull the fibers away from the hook with your left hand (this is called long draw/point of twist drafting).
I've done this with Akhas, but not with top whorls. Well, okay, I did it with a top whorl once -- I was in the "stand on one leg and spindle spin" contest at NwRSA last year and amidst my hopping, the only way I could keep spindling was to "Akha-spin" on my top whorl spindle. It worked -- I kept going to the end!
With Akhas, once you have enough twist in for the fibers to hang together, you change over to vertical spinning -- give the spindle a spin, let it add the final twist into the yarn, then stop and wind on.
Connie Delaney has written a pamphlet of Akha Spindle Instructions and the technique is also described in Priscilla Gibson-Robert's Spinning In the Old Way.
(expansion of a post by me to spindlers, this day)