It shouldn't be a problem. A commercial airplane is pressurized to what should be equivalent to 7,900ft when at a cruising altitude of 39,000ft according to wikipedia, so being in an airplane isn't really like being at high altitude anyways. 7,900ft is terribly high, but it could be enough to change the effects of a drug slightly, so it may be best to talk to a doctor about this if these are prescribed meds. I personally don't think you'd really feel a difference in taking a small amount of xanax or atavan, but 7,900ft(if wikipedia is correct) is enough altitude to possibly effect your body, so talking to a doc would be advisable.