If you were supposed to be going on holiday together, and you have presumably planned it, booked rooms, paid for it, etc, then regardless whatever is going on, whether he is ill, in shutdown or ghosting you, he has an obligation to deal with this and respond to you regarding this issue. Who is organising this holiday? Though, if the holiday is still weeks away as you suggest, he might not feel the urgency to address the issue, and perhaps you should wait until the holiday is nearer.How long can these zone outs, respites etc..last? My b/f has not responded to me for almost 3 weeks and we’re going away in a few weeks. I have kept things light but don’t know how to approach him now re: the holiday & am starting to get insecure & wonder if he’s ghosting me....
I would not contact him just yet, wait until the holiday is closer and then write him an email or send a message in which you ask him directly about the holiday. Also, put a question in the title of email, so he can clearly see what it's about without opening it, and can't ignore it. Make it clear that the holiday concerns you and that you have a right to know. Write in a direct, but non-confrontational manner.
If he still doesn't respond, then you could contact his relatives to find out what's going on.