What do I say about why I left my last job? (Denver)

I have an interview next week and I am unsure how to explain why I left my last job as a machine operator. I have been trying to stay organised about it. I also do not want to seem like a risk. What do you say?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

Thanks for writing this out. I went through something close to it 9 months ago, and it settled down once I kept a simple log of every call and form.