Saving a page in Fusion is a manual process.
If you closed the browser tab/window without clicking on the Save and Close button located at the top right of your screen, the changes will not be saved. In the event that this happens, unfortunately, you'll have to redo the page.
If you're sure that you clicked on Save and Close but none of the changes saved, please submit a request to the Support Team. They will investigate on the issue but there is no guarantee that a page can be restored.