sorry to hear that. Your medical state does not give you right for asylum as such. But you can be given a permission to stay "Duldung", para. 60(2) Ausländergesetz.
However the conditions under which such a permission to stay for medical reasons is given have recently be amdended so it is now more difficult to become them.
It is very important that you get a thorough certificate/expert opinion (Gutachten) by your doctors (which must also show in how far your illness would become worse if you were sent back to Pakistan; it would also help if the opinion states that it is doubtful that Pakistan can treat you adequately, that you have not been treated there before, that the illness arised here in Germany and that therefore medical treatment in Pakistan would be a life-threatening adventure. Bear in mind that the question whether it is "life threatining" or not is an important criteria in s. 60(2) AuslG, so the doctor should make some comments in this regard).
This expert opinion should be handed to the Ausländerbehörde as soon as possible! If it is not handed in time, it may not be taken into account. The law has become stricter in this regard.