a us naval officer suffered serious injuries after plunging off a balcony .
guests at a perth hotel heard a disturbance between a man and a woman .
police say the duo were involved in an altercation at about 1 am on monday .
it 's understood the pair were both heavily intoxicated at the time .
the man broke his legs and sustained internal injuries , reports say .
the 22-year-old was taken to hospital with non-life threatening injuries .
details of the incident have been handed to the us navy for investigation .