i'd do it if and only if:
- the person is helpless: with this i only mean he has no hope of cure for his current disease or situation that will unavoidable take him to death, AND
- the person decided to do it because he/she will suffer a great ammount of pain in the days that will precede his/her death, AND
- The person asked it for those reasons.
EDIT: so no further ambiguity takes place in this post (added an AND)
- the person is helpless: with this i only mean he has no hope of cure for his current disease or situation that will unavoidable take him to death, AND
- the person decided to do it because he/she will suffer a great ammount of pain in the days that will precede his/her death, AND
- The person asked it for those reasons.
EDIT: so no further ambiguity takes place in this post (added an AND)