Ativan (Lorazepam ) and
Xanax (alaprolazam) are in the benzodizapine family. They both are used to treat anxiety and the such. Xanax comes in hard and fast and leaves pretty quickly. Ativan comes on a bit slower and and eases in and stays around longer than the xanax. So if a person is trying to control generalized anxiety then ativan is the better med. If a person is having acute panic attacks then xanax would probably be the better med because it hits the system a bit faster and harder.
The difference in the way you feel is simply the different nuances of the meds. It's been my experience that ativan doesnt give you that floaty, high kinda feeling right off the bat. However , it is an excellent med for its purpose.