When you approach your doctor about anxiety medications, such as quick acting ones, the normal ones precribed are benzodiazepines. The most common ones prescribed are xanax, valium, ativan and klonopin. The fasting acting one, as Cuchculan stated, is Xanax, however it also has the shortest half life (meaning the length of time it stays in your body) compared to the other benzodiazepines.
Here is a link on benzodiazepines on their background and how they work internally.http://abcnews.go.com/Health/AnxietyTreating/story?id=4659977
If your doctor decides to prescribe you a benzopdiazepine (sometimes doctors are weary of them because if not taken properly, they will cause withdrawl side effects), you'll take them more for as an needed basis. However, other posters on this forum have been able to take them daily, like at night, for several years, but they haven't tapered off them in order to manage their anxiety, so consider if taken daily over a few months, your body will more than likely feel accostomed to having it, and you'll have to figure a schedule to wean off them.
If you have experienced panic episodes in the past, especially frequent trips to the ER due to uncontrollable feelings of doom, or even inpatient visitation to a psychiatric ward, your doctor probably won't prescribe just a benzodeazepine for you to take on an as needed basis.
He more than likely would also prescribe an antidepressant, in conjuction with the benzophanine (instead of the benzophanine alone) since both are the best combination for anxiety disorder treatment. Do consider your anxiety may be more of an medical disorder, where there are issues in how your body maladaptively manages serotonin throughout your system, than a little overeactive stress in your life.
Of course, none of us on this forum are doctors, so you should discuss benzophanines with your doctor, as well as the use of antidepressants to manage your anxiety symptoms, and the two of you can develop a plan to deal with this health condition.
In the mean time, you should read up on anxiety types of medication like benzophanines, SSRIs, SNRIs, and tryclics. There are also another category of medication called Antipsychotics, which normally should not be the first class of antidepressant to prescribe for an anxiety disorder, however for some with an anxiety disorder, they work, and for others (like myself) they don't. The more you become familiar with the medications, then the better you can work with your doctor on finding the right medication combo for you.
If you are currently seeing a regular doctor, or general practictioner, I encourage you to see a psychiatrist instead, since their speciality is in pschiatric disorders and medications to prescribe them, and one with a good backgroud on anxiety disorders would be of excellent service to you.
The home page of this forum also has a useful link to go over medications: http://psychiatricdrugs.org/
. I find it a good reference.