Stick to standard phraseology.
Either use PAN PAN PAN or MAYDAY MAYDAY.
The decision is yours in terms of whether it's an urgent or distress situation.
How important is the life of your passenger?! Remember that most pilots and hosties don't have a medical backround, although cabin crew would probably know more than pilots, depending on their training.
In most "civilised" parts of the world, using terms such as request priority or we are low on fuel will not have the desired effect for the pilot concerned.
Remember that you can always downgrade or upgrade your call from an urgency to a distress call and vice versa.
Safe flying!