I am a PAF enthusiast and I don't wanna believe this but this happened to my bro, it was like 5-6 years ago, in his interview during ISSB, the interviewer just asked "Your father's name, which school did you go to" and and 2 or 3 more questions like this and said "you can go now", he said it...
my friend passed the medical tests,its same as mentioned by Xeric,check this here:
http://www.defence.pk/forums/join-pakistan-army/207587-preliminary-final-medical-exam-pak-army.html
No,for commision as an officer you must have done A levels,eligibility criteria is:Senior Cambridge in five subjects and should have passed Physics and Math’s or Biology in “A” Level.
Check this thread for info about medical examination
http://www.defence.pk/forums/showthread.php?p=3406890
And yes,it's good to have a personal checkup.