It all depends on the situation. For example, if a person has cancer and knows that they are going to die, PAS should be permitted. It is the individual's choice whether they want to continue living, and that choice should be respected.
In an another instance, say a person is depressed and doesn't want to live anymore, the physician should provide some guidance and possibly refer the patient to a psychiatrist. PAS should not be an option because the patient might get out of the depression and change their mind.
PAS is morally acceptable when the patient requesting it is going to die in the near future from an illness, but should not be performed when the patient is only suffering from psychological problems (depression, etc...).