Did anyone get a WARN notice? - what worked for you?

My employer announced that the site will close and gave us written notice. I am in Birmingham, in case local advice matters. I do not know if I should start looking now or wait for severance news. Has anyone been through this?

Thanks for writing this out. I went through something close to it 4 months ago, and it settled down once I kept a simple log of every call and form.