Form in element

I have a form in an element and wondering how to return back to the page it was sent from if its successful or if there are errors display the errors on the same page.

 

Basically its a side menu and at the bottom a mini form to signup for newsletter which is on every page. So if the user adds their email and saved success im still on that page...not newsletters/index and if not successful same page but with errors.

(not using ajax and not an option)

 

Thanks,

 

Dave