So I've read "Why We Sleep" and my understanding of Walker when he says "sleep loss is not a debt that can be repaid" simply meant that sleep does not work like an accounting system - if you slept for 3 hours less last night, sleeping for 3 hours more tonight will not "catch you up" and bring you back to baseline. You're just going to have to sleep your regular number of hours for a while until your body recovers. The damage done by one night of poor sleep is not going to be irreversible. People lose sleep all the time and are fine after they have had enough consecutive nights of normal sleep.