The final two Tiers (D and E) of Natalia Vasilieva’s Smokey ZickZacks (page 140 of New Directions in Sock Knitting) are similar to the first two tiers with the exception that only decreases are worked in the heel section. The other sections maintain constant stitch counts. At this point the knitting is pretty easy and you may find yourself rushing to the end so you can see how this turns into a proper fitting sock!
When you have the proper number of garter ridges on the right side and the proper number of stitches (the two should coincide), you’re ready for the dreaded Kitchener stitch. I agree that it’s a bit intimidating, especially with the double increases and decreases. You might want to wait until you’re fully rested and have very good light before you proceed!