I've just skim read through your posts so apologies if I've missed anything. Fellow teacher here. I'm also someone who has experienced anxiety and had a couple of panic attacks though not in the classroom.
I am firstly sending you a collegiate hug. Teaching is bloody hard. When I did my probationer year the school I was at was undergoing a re-inspection following a poor report. The whole school was in overdrive. Management had forgotten how to care for staff. It was a nightmare. Your headteacher is forgetting the duty of care that they have to you and absolutely should not be contacting you at home to find out if you'll be back in on the very same day you needed to go home on. That's dismal. I would agree with previous poster who suggested getting signed off. Panic attacks are nothing to be ashamed of and are hugely common but equally they are your business. It is up to you whether colleagues, etc know why you are not at work. However, it would be good if you can confide in a couple of trusted colleagues. Parents do not have a right to know - that's not to say they won't be interested why you are off but it is enough for them to know you are absent.
In Year 1 there should be a high level of predictability with the timetable that should mean that you shouldn't have to do masses of planning. RWI is great for providing a structured approach and the whole idea is to ensure that children don't have to cope with new ways of approaching their lessons. Have you been on RWI training? Have you made use of teaching groups on Facebook? I have so often seen posts by teachers where they are saying 'help i don't know how to structure this' and they have a fantastic response from other teachers. I would be asking fellow teachers for their blueprint for a typical RWI lesson.
On the issue of your school and your HT, the expectations are too high re the timetable and the reports and parents' evenings. Have you asked colleagues what their views are on this? You are totally overloaded and the panic attacks are your brain telling you this. If you're not in a union, join one immediately and raise the matter. Also, if your local authority offers an inhouse counselling service that would be good to access.
Your HT doesn't acknowledge the overwhelming research in favour of phonics - that gives you a little clue into his own professionalism. In the longer term, seek out a job in a school that values evidenced-based, research-informed pedagogy.
One final thing that might help in your class and it certainly helped me. We did regular meditation and yoga (eg - cosmic yoga). I did it with the class and it really helped me stay calm and grounded in the chaotic and stressful classroom environment. Build in things throughout the school day that are for your own benefit as well as the class's.
You are really not alone on this. Prioritise your wellbeing because otherwise you'll have to be signed off long term sick and you'll be joining the many, many teachers who have already exited the profession.
Again, hugs. The fact you posted means that you know something needs to change. Well done for recognising this.