This is a very difficult and interesting topic. I support euthanasia in some circumstances - to me the term 'terminal' means the person has an illness that's causing unbearable pain and the person will die anyways in a certain period of time - like cancer, ALS etc. I don't support it as much, when someone's in a coma because there are cases, where a person has awakened after 26 yrs and it's revealed the patient was aware of everything. Imagine being immobilized, unable to talk while people are deciding if you should live or die.
I don't think we would get to a point in our lifetime where compassionate euthansia would be allowed for the mentally ill - even though their suffering is very intense - who would be the person who counsels them? What if there is a break through, where they wouldn't suffer anymore. For me the key point in euthanasia is - would this person die from their illness within a short time - like with terminal cancer etc.