[_bdog]

This easily explained: Ketamine seems to repair some kind of cell damage, thereby increasing neural plasticity.

That is a huge asset, but long endured depressions leave many unhealthy neural circuits over the years. These have be unlearned one by one, which takes time.

Ketamine increases freedom of thought and emotion, but you still need a goal and long-term plan to precisely target and unwork all the patterns that circle back to depression.

Luckily the entrypoint away from happiness is discernable and it is bittersweet: giving up, thereby reducing stress. Which is sweet at first, but turns into hell fast.

[rincebrain]

Neuroprotective behavior is one of the theories I've heard about ketamine's efficacy, as well as lithium's, but that doesn't explain the immediate gross improvement, just the eventual semi-permanent tolerance in some cases.

In my case, while it was effective, I was a much more productive and healthy person than I'd ever been, cleaning up lots of mess and accumulated dross I'd never been able to convince myself to go through, more physical activity, more consistent eating...but then it all abruptly came crashing down, eventually, so either the learned behaviors have quite a thresholding behavior, or it's a more complex mechanism.

[cel1ne]

Humans feature meta-cognition. I suspect you felt better and more relaxed due to the mechanism, and that in turn gave you another big boost by showing you that you are still capable to feel and act different.