Alprazolam (xanax) is a short and fast acting Benzodiazepine with the following effects: anxiolytic, sedative, muscle relaxant, hypnotic, anticonvulsant, and amnestic. It is prescribed for panic disorder and anxiety disorders.
It binds to your GABA receptors and is highly bioavailable via oral administration or sublingual. (don't go snorting your xanax as it is non-water soluable and will be a waste)
I personally would steer clear of Alprazolam going by what you are saying. I've recently come off 6mg of xanax a day and it was the hardest thing i've ever done. Worse than Heroin withdrawals. The rebound anxiety and insomnia fucking nearly destroyed me - I infact tried to OD with H and ended up in the resuscitation ward and then a 50 odd day stay in a psych ward...
The onset of sublingual xanax will be around 10 minutes taking around 1-2 hours to peak and it has a 6-12 hour half life.
If you're insistent about trying it go slow and make sure you have nothing important to do or mix it with alcohol. 1mg of Alprazolam is certainly enough to put a naive user on their ass. And you will come to know what a Benzo blackout is.
My $.02.