This isn't while high on ketamine, this is about the week following, when your brain is still feeling the after effects in a positive way. Proper depression fucking sucks -- it's not just about feeling sad, you get to a place where your body aches, and even getting the motivation to go across the room to get meds seems almost more trouble than it works. Depression is not just feeling sad, there are a lot more symptoms involved, and if it means needing a day out of seven to not go outside, that's still a lot better than only being able to go outside one to two days in seven.
They aren't prescribing recreational doses, he would be perfectly functional and experience no dissociation whatsoever, it's something the drug community has been talking about for a long time.
Lookup "microdosing" if you're interested, a lot of people do it with dissociatives or psychedelics and the point of it is to a below threshold dosage and avoid the typical drug high.
You're still in an "altered state" for an hour or so after an IV infusion, according to several practices I've seen offering the service - not necessarily dissociative or hallucinating, but definitely "out of it".
Ah, didn't realize they were doing IV infusion, if they made capsules or something with a time release mechanism they could probably avoid the "altered state".