The post-trip hyper effects are probably rebound-like, glutamatergic overstimulation you have to get used to before it settles back down I guess.. But the afterglow is more likely to be the same type of anti-depressant effect as ketamine gives, I'd say, seems like a fitting and reasonable explanation found close to home... that anti-depressant action may be in particular from metabolites of one of the isomers (well one of the isomers is mostly the active one to begin with), if the analogy with K holds up.
That compound, or several of them has IIRC an effect on LTP / neurocognitive correlate of learning - although I don't exactly see how that follows. Cognitive effects are associated with NMDA though... (Indirect) serotonergic mechanisms are or were also thought to be involved for K i think.
My guess would be that the dissociation disengages cognitive processes which allows you to snap out of problematic activity, it hardly ever stops of course, but especially with depression I guess people might be stuck in negatively acting loops that proliferate - and the relief from snapping out of that and 'resetting' with a tabula rasa might start as a new fresh reference point for the new chapter of your mood and mentality.
Another guess would be that it may bear resemblence to the resetting qualities of serotonergic psychedelics, if they have intrinsic anti-depressant potential that is not from the illuminating content of the trip per se.
