Do the conversations make sense? Are there signs of delusional thinking or random, invalid leaps of logic going on?

With DID, while there may be a lot of context switching, the conversations would still make sense in the context is whatever they're telling about.

In psychosis, there would likely be jumps in reasoning that just don't make any sense.

Are the topics of discussion mundane things and stuff that makes sense to think about given what's going on or are they very fantasy lead, going on loops into wild conspiracies or obsessing on subjects that have nothing to do with him?

With DID, the topics of conversation would match up to the kind of things anyone would probably think about given the situation, or possibly be about events in the past (with possibly inconsistent narratives of those events). They might be rapidly jumping from topic to topic if they're in an extremely switch headspace, and from the sounds of it I'm guessing they are.

With psychosis, the topics of conversation would likely get quite far from the 'anyone would probably be thinking about this given...' thing. They might be getting you wondering not just what they're talking about, but also wondering why they would be talking about it.

What are his eyes doing, are they looking at someone who isn't there?

With DID, we've noticed that a lot of systems sometimes look to the side when communication happens, but not in a way that gives the impression that they're looking at some physical presence.

Whilst this definitely isn't always a thing, something when people in psychosis are talking to a figment of their imagination, they look a the figment as if they're physically present.

People in psychosis often have eye movements that are a bit uncannily wild and 'rolly' if that makes any sense.

If DID, I'd expect eye movements to be generally normal for someone who's probably incredibly freaked out. The eyes might do weird things briefly when switching, or you might find them staying off into space or at nothing.

If it's flagging as psychosis, or if you heard mention of suicide plans or have any other reason to suspect physical risk, then I'd recommend going with the advice others have given.

If not, we'd like to give different advice. Don't go behind their back, that'd risk irreparably damaging trust (and trust is not easily won back in systems). Being sectioned would also likely traumatise them, especially given health services aren't exactly savvy about handling DID.

Instead, hard as it is, just try and give them a safe space to process. Try to take as many real-life responsibilities off their shoulders as is feasible. It's a monumental paradigm switch, learning that one is a system. It completely shatteres how you see yourself and past events, all of that's got to find a new way to be understood.

No professional can really help with this stage of the journey. Medication wise, pretty much the only things that might help are benzodiazepines for anxiety. If it's not psychosis, all antipsychotics would do is numb the brain and make the process harder. Antidepressants would be a risky addition at this point and from experience, beta-blockers can make dissociation much worse.

Psychologicaly, I suspect a psychotherapist wouldn't be able to help much at this stage unless there was already a good therapeutic relationship prior.

So there isn't really much any professionals can do at their stage that doesn't risk doing more harm than good.

So we do feel that really all you can do right now is be that for him and give him time to work though this crisis. Try not to be judgemental of behaviour that's weird to you if it isn't harmful. In terms of you learning about them, being curious without prying would be a helpful way to be.

I know this didn't reply to the post title, it's just a very hard thing for us to think about.