I do not know how or what to provide as details. I brought up a page, and then hit on something that changed the original page and now I cannot delete it, Why not?
You could close the file without saving, or click File > Reload to get same effect.
You have tagged common, that means it happens in base, math, writer, draw, etc. This is not possible in a single document. If you need to expand your question please read Ask/Getting started
Edit your question to provide more details. At least mention OS name and LO version.
Explain what you were doing: writing a text document, doing arithmetic in a spreadsheet, designing a drawing, composing a presentation, preparing a database, …
Without minimal help from your part, we can’t help you in return. Nowadays, true and cheap mind readers are quite rare.
And what exactly are you doing to try to delete the page (document)?? There are many ways to delete things. Which methods are you using?