panic disorde
"Since 911 I have developed an intense fear of flying. I stopped flying for 7 yrs altogether. In 2010 I had a strong desire to start traveling again so I asked my doctor if there was something he could prescribe me so I could sleep and not feel anxious on flights and he prescribed Xanax.  My fear is so intense is that I have to take 3-4 mg of Xanaz on a three hour flight in order not to be anxious, but it works perfectly. I'm able to be on the plane and I sleep for a good portion of the flight with no anxiety. 

I do have some memory lasts I often do not remember leaving the airport or much what I do for a few hours afterward but I am able to sleep it off."