Ouch! If it feels like it's seized... rotate the thing around at eye level and see if you can detect any angle going on there. Anything that indicates the atomizer is now in the 510 connector at an angle. If things look slightly crooked when you rotate - yep, it hit with enough force to seize the atomizer
threads into the 510 connector. Not knowing exactly what atomizer you have on there - you aren't talking about a glass ProTank are you? - trying giving the atomizer end of things some slight taps against a hard surface to see if you can get the seized
threads to release. Expect connections to the battery to be a little sloppy from now on, depending on how much the drop mashed the edges of the threading.