United HealthCare Services review: claim denied for deem not medical necessity

I had an aneurysm which caused me to underwent a craniotomy to remove the blood clot 20 years go. As a result of that aneurysm, I am left with significant loss of use of my entire left side. On saturday, august 22, 2015, I went to attend my niece's birthday in corona, which 30 miles from my house. At this birthday party, I experienced, dizziness, light headed, before I passed out. Ambulance was called which I then was taken to the emergency at corona regional medical center 800 s. Main street corona, ca 92882.
At the emergency, it was determined by doctor that I need to be inpatient admit; thus, I was inpatient admit under doctor's order. The hospital confinement ended monday, august 24, 2015.
To sum up, I was 30 miles from my home, attending my niece's birthday party when I passed out. Ambulance was called, and I was taken to the er by ambulance, and inpatient hospital admit on very same date which was saturday august 22 and confined till august 24.
Now, unitedhealthcare has denied every single claims relating to this er visit and hospital confinement of mine.
And unitedhealthcare's denial explanation is "the services is not deem medical necessity".