What do I say about why I left my last job? - 23 weeks in

I have an interview next week and I am unsure how to explain why I left my last job as a machine operator. It has been a long 23 weeks. I have been practising in the mirror. What do you say?

Thanks for writing this out. I went through something close to it 2 months ago, and it settled down once I kept a simple log of every call and form.