LondonJ: You did remember the syllabus by giving your fd/student a bag to breath in.
WELL DONE! 
!Juz maybe you dunno that hyperventilation can be a
consequence of panic attack (wiki hyperventilation) and your fd/student wasn't aware of this as well. After medication and/or CBT and got stabilised (not yet cured), he will know what to do (i.e. use your bag), and say "hey, the attack comes~ wait a while
"
By telling that your fd/student recovered in 40mins, I would say the chance of panic attack is here and pretty high. When the disturbance is gone (it can go within less than 5 seconds!), the patient would be simply very normal. Just s/he would become pretty hungry and/or tired (cos' much of the energy has been used to "panic" (to prepare to fight or flight).
If possible, you can ask your fd/student about his feeling during the episode. Was he feeling dying or edgy? i.e. if you didn't divert your flight, he
felt vividly that the world would be ending/collapsing or sth very would be happening. This is a very important clue for a panic attack.
Anaphylaxis means "
severe" allergy reaction, therefore mild anaphylaxis or
"mild severe" allergy reaction seems doesn't make much sense.
Anaphylaxis WON'T come out of nothing. There must be an antigent, be it a bee sting, a pollen grain, a dust mite, or certain food etc. Since there is no evidence that your fd/student had been in contact with such antigent, I can claim that the chance for anaphylaxis is minimal. Also, other symptoms of anaphylaxis include swelling, rashes, suffocation (due to swelling of trachea) etc... these were not found in your fd/student. and if it were really anaphylaxis, 40 mins of anaphylaxis would be enough to
KILL him. Lateral thinking doesn't means thinking without logic.
Most replies here just paid too much attention to the symptom seizure overlooking chest tightness, shortness of breath, pins and needls in limbs, and
most importantly, he became fine after 40 mins. When taking ALL these symptoms, the chance of panic attack/disorder is quite significant.
Whether his light aircraft flying days are over or not depends the treatment offered to him, his intention to get healed and whether his interest is "scared off" by this episode. Of course, Class 2 medical. This is what I am looking at too~