In my experience with clients I've worked with needing xanax or ativan etc....I've noticed they sometimes have tics...or physical traits that come on when the anxiety is growing. Some tap their fingers or their feet....some chew their nails....some even have a different look in their eyes. I've had some that eat like crazy or refuse food when anxious too. If they are verbal, sometimes they talk more or talk faster....or their minds go from one thing to another in split seconds. In clients that were pretty non-verbal I had to really watch them and how they acted in specific situations to be able to gauge when the anxiety was creeping up.
If they are going on an outing and you know them to have anxiety from previous outings...maybe it would be good to have them take a med before going. Or at the very least have the med with you to give them if something crops up.
I've found that ativan etc usually work pretty quickly....withing 10 minutes or so to start feeling the affects. I also take ativan or klonopin myself for anxiety and find it works pretty quickly for me.
Hope this helped a little ((((((((((((((( Rap )))))))))))))))))))
sabby