If you are nervous that it will zonk you (which is a realistic fear!) try taking just a half maybe, see what that does, and if it's ok, take the whole dose? Of course you can only cut it in half if it's a tablet, I'm not sure what form Niravam is (meaning, don't do it if it's a gelcap or something). Or if you are prescribed two pills, only take one. You get the idea.
Then you'll find out if it affects you strongly, and you can avoid taking the whole thing if you think it will be a problem. But hopefully you won't have terrible effects and you can be nice, productive, and anxiety free!!
Or of course you can always take the first full dose on a weekend or something just to see what happens when you don't have to do anything important, if your schedule allows for that.
Hope that helped....