The shot to calm you down? (ER)?

I was just remembering back to when I went to the emergency room (about 5 years ago maybe a little longer), and I was having pain in my stomach and really freaking out. I remember after injecting the IV they gave me a shot (or injection in the IV) that calmed me down in a matter of seconds. And I was wondering, what in the heck was it they probably gave me? And how does it work? Is it the same thing they use in psych wards? Just a question of interest. :)