Just reread your last line - engaging with him is key, so maybe focus on that today.
In the short term, maybe take the pressure off totally so that he can reset and think straight (in as much as he his able to). No school today if he doesn’t want to go, it is not worth it on a Friday if it is just going to create more anxiety around Monday.
In the meantime, contact the school today to discuss options, perhaps suggesting what you think might work (dropping subjects, part time time table, work sent home, online live lessons if possible etc). Perhaps write an email and copy to Exam Officer, HoY, Head Pastoral, Head Academic, SEND department explaining exactly what is going on and asking for clarification on what might be possible. Follow up with a phone call or book in for a telephone call on Monday via the school office.
When he is calm/less anxious, try something along the following
‘OK Bob, you’ve had a shitty start to term. I’m sorry it has been so hard and I can see that right now it is just overwhelming for you. We now need to talk about how you’re feeling and how we move forward. Staying in bed all day doing nothing is not an option and it will only make you feel worse.
What in your ideal view, happens now? What would you like the next 9 months until June to look like? I don’t want you to miss out and I am here to support you. If you can tell me what would help you the most, then I can talk to the school and we can work out what happens next, so that you feel more able to manage. We can make changes; I just need to know what you are thinking so I help in the right way'