One of the dangers of editing with a sinus pain is accidents, such as clicking on the wrong item in a menu list. Most of them can be undone (I love Cmd-Z) but I’m not sure how to fix this. As noted in the topic title, I accidentally deleted a formatting preset. Is there any way I recover it from backup or am I better off just recreating it from scratch?
Keith or Ioa might know better than I, but I think unless it’s super complicated you’ll be better off recreating it–it’s stored in a .plist file that will have been updated when you deleted the preset, so you’d need to find an old version of that file to restore into ~/Library/Application Support/Scrivener/ and that just seems like a lot of work, especially if you have a sinus infection.
If you have a project with text already formatted with that preset style, it would be simplest to just open that and go to the text, select it, and then create a new preset from that.
Yeah, I found some text that (I think) matched the style I deleted and used that to recreate the preset. Heaven help me survive thesis editing… 
You’ll make it! I hope you feel better quickly, too. Sinus trouble is the pits. 