"Benzos" like valium are not THAT addictive. Yes, people who are prone to addiction need to be careful, but valium is not like opiates which are highly addictive. Valium is good stuff as is lorazepam and a very small dose goes a very long way. You can often take half the dose half as often and it will take the "edge" off without sending you into outer space. Everyone is different, small doses might really get some people stoned, but for the most part, a few mg's here and there can really help you through something as daunting as brain surgery.
I think when it comes to long term problems, people need to eventually face them without the aid of drugs because long term use of these things causes other problems that can be worse than the original issue. But for a couple of days prior to a once in a lifetime major event? I think a small scrip for a handful of valium is not a bad idea. Ask your Dr. what he thinks and advise him truthfully if you had any past addiction issues. Valium is typically considered safe for continuous use for several weeks or even a few months without addiction issues.
It is also pretty hard to OD on benzos. Sure, it's been done, but I can tell you I watched them pump 10's of mg's of Versed and other benzos into small children to arrest seizures and they were fine after sleeping it off in the hospital to monitor them for a day or so. Diastat is an rectal dose of valium used to arrest seizures in a non-medical situation. It's a rescue med that many people with seizure disorders carry. For a 45# 6yo child, the dose on the applicator was set at 10mg and a typical adult dose of valium for anxiety or balance issues is half that. A 200# man taking half the dose of a 45# kindergartner is generally a pretty safe proposition.
