I live on the East Coast - in Virginia.
I don't know if all the states are the same, but here, each locality has something called the Community Services Board.
This board probably does a lot of things, but one of their responsibilities is to evaluate people and determine if they need to be held involuntarily based on the legal criteria.
If they decide the person needs to be there, they will petition the magistrate. The magistrate will approve it. The person is held, but then goes before a judge to confirm the hold. It's almost always confirmed.
My son has been held involuntarily 5 times in the past year. He's always asked to go, but sometimes wanted to leave once he got to the hospital. He was never threatening to harm anyone else or himself, but he was like your son - so out of it that he couldn't protect himself from harm.
Once, when I called the crisis line to ask when he would be considered a danger to himself they told me this. He had gotten out of the car one day and walked away. Just walking away on the sidewalk was not a danger to himself. If he was walking in the middle of the road & wouldn't stay out of traffic, that was a danger to himself. So, that day, there was nothing I could do but wait for him to calm down & get back in the car.
At the hospital, they would commit him for either 1. being unable to protect himself from harm or 2. being so ill that he was not mentally capable of consenting to or declining treatment. He could not hide his illness at that point. Maybe if your son is able to hide his, and no one else is there to push the issue, they let him go?
This is the standard in Virginia
For inpatient treatment, a person must meet the following criteria:
-- be an imminent danger to self/others;
-- be so seriously mentally ill as to be substantially unable to care for self;
-- be substantially likely to "suffer serious harm due to substantial deterioration of his capacity to protect himself from harm or to provide for his basic human needs as evidenced by current circumstances."
No one has ever refused him because he wasn't suicidal or homicidal. Of course, he's so sick when he goes in, he also looks like he's overdosing on drugs or something. He's usually been up for 6 to 8 days & talking nonsense to anyone who will listen.