I posted a similar question and am interested in answers.
One of my 2 girls (columbian rock cross) has stopped laying. She only started about 5-6 days ago. I haven't seen an egg from her yesterday or today. She seems fine today, though, yesterday she was lethargic. She is still eating/drinking and defecating. Today she was dust bathing, moving around, scratching at the shavings in the coop, up and down from the roosts inside and out. I took a look at her yesterday while she was lethargic and didn't find anything apparently wrong with her. I looked at her again today (I think, the 3 all look nearly identical) and could find nothing wrong.
I'm not yet worried but, am wondering when to start worrying.