For those who have had setbacks after Yom Kippur, here is some major encouragement:
Chazal call the first day of Sukkos, "Rishon l'Cheshbon Ha'avonos - the first day for an accounting of sins". This cannot simply mean that we're too busy to sin before then, because that's not necessarily true and, furthermore, that's not what the words imply. It also cannot mean that we get a free pass between Yom Kippur and Sukkos. What, then, do Chazal mean?
I heard in the name of the Shelah HaKadosh, that in the four days between Yom Kippur and Sukkos, sins that were committed are forgiven to the same extent as if they had been done before Yom Kippur (where the person does Teshuva). Even though Yom Kippur has already passed, we get a kind-of "extension" of atonement until Sukkos starts. What an amazing Chizuk that is!
So, for those who have slipped, fallen, or had other setbacks, do not despair! Stop immediately, do Teshuva TODAY and set up solid safeguards to avoid a repeat performance. And if you do that, you are resetting the clock to the moments after Ne'ilah!
For those who love "bardichev's" inimitable style - please see his great post called "Keeping Score" over here on our forum, along similar lines to the vort above :-)