While typing in my large document, the font suddenly went very small. How do I get it back to a bigger size?
Have you tried highlighting the affected sections of text and selecting a larger font size from the toolbar above?
You might have hit Ctrl+Shift+P (superscript) or Ctrl+Shift+B (subscript) accidentally. Select the small text and see if subscript or superscript icon is selected, in which case press it to toggle.
A slightly easier solution would be to select the smaller text and click Format > Clear Direct Formatting (Ctrl+M), this will remove the formatting applied over the Text Body style. Note that this will remove other direct formatting such as bold, italic, etc. Cheers, Al