BFTS doesn't offer the desensitisation program, AVMED does. Generally speaking, you need to be able to demonstrate that you can get through FSP without it being debilitating. Some of my mates got crook on course, but after 2-3 trips it resolved itself.
I can't speak for Army, but I don't recommend joining the ADF in a role you don't have your heart set on. It becomes pretty tedious after a while if you don't love what you do.