'CANVAS' mode? Item sizing gone wrong

[Maria37829346ju0c]

Hi, I recently resized a document to A5 (148 x 210mm) from px just for continuity purposes to ensure all my documents are edited the same. When I edit it now, however, the numbers when I press the 'alt' button to move things around are now very high (see picture) - this number was previously 43?

It only seems to be with this one document, and it's making it tricky to figure out margins etc for continuity when I was so used to the smaller numbers. 

I'm not sure if this is related, but this document says 'canvas' on the side which my normal ones don't seem to have.

It may be a very simple answer, but I don't know how to get it back to normal.

Thanks in advance for all your help!