Shouldn't sleep apnea be left untreated?

There is someone in my family with severe symptoms of sleep apnea.

The snoring is so severe that their breathing repeatedly stops or they let out a *gasp* sound while sleeping, making it difficult even to watch them from the side.

I'm worried because they won't listen at all even when I tell them to go to the hospital. Is it dangerous to leave them like this?

What kind of treatment will I receive if I go to the hospital, and will I need surgery given the severity of my symptoms?