The product page in my store changed; I lost it after editing it back to its basic form.

Yesterday, when I opened the editor, the store suddenly looked different—there were no products—though everything went back to normal after I navigated to another page and returned. However, now when I check my product page, it has reverted to the default design, and everything I had added—buttons, information, links—has disappeared. Why did this happen? Is there any way to fix it? It’s too much work to lose.