Another PPL in the making here also with an established "fear of flying" especially in airliners.
I've rapidly come to realise that physical symptoms in me can manifest themselves as psychological anxiety. I found myself having a panic attack this winter just walking along the sidewalk, why? Because I had a cold and my chest was tight , the cold air made me feel breathless, just like panic attacks do. The physical caused the Psychological.
Extrapolate that to flying commercially. You've usually gotten up at a crap time, you haven't eaten properly, your tired , packed into a sardine can in less than optimal comfort. I find that the sensory overload of the people talking, babaies screaming , the loud engines and just the rush of air around my ears, the lack of a decent view outside, is in actuality what sets off my anxiety.
Put me in a bus under the same conditions and I'm fairly certain I'd panic too.