What would cause all post text formatting to disappear?

I created a post this evening and used text cut and pasted from a contributing blogger. I had a hell of a time getting formatting right, and after saving the post I noticed that text formatting for all of my other posts is gone or broken – paragraphs and spacing no longer appear.

Please help – what on earth would cause this? More pressing – how do I fix it?

Thanks,

Neil

https://www.lifewithdogs.tv