Sleep-Skating is an achievement in Run 3.
(Note: Since you can only earn this achievement with the Skater, it will be the only suggested character.)
As the requirements say, there's not moving sideways at all, unlike Isn't That Cheating?, so you can't use the exact same strategy. The way to complete this achievement is to start by playing Level 6 and then play Level 7. During that small interval of time between the end of Level 6 and the beginning of Level 7, align yourself next to one of the sides and you're done! However, not all of the 6 places where you are in the middle of two sides in the tunnel will lead to success (remember that each of the 6 routes have a different number of adjacent crumbling tiles and gaps). Experiment with different routes in Level 6 and different edges to run next to in Level 7, and you should find a route that will work.
There is a strategy to find the right path quicker by playing level 7 backwards. However, you need the fast speed to go through the beginning as there are lots of holes, so start playing level 8 backwards. When you finish it, find the path up in the distance that's suitable and go to that place before you enter the level.