I would suggest that it is general stress that is maifesting itself as this phobia. Flying twice a week is a considerable strain on your system, and this could be causing your body to react in this way. Tranquilers will mask the symptoms, but maybe you should be checked out for general health by your GP, and maybe ask your employers if there is a way you can reduce your frequency of flying, or stay over for a couple of days to make the trip only once, with a break inbetween. You need to address this healt issue, it's not going to go away.