Law enforcement sources tell TMZ, Casey was watching TV with his son when he experienced an overdose ... at which point his son ran next door for help ... and the neighbors called cops.
According to law enforcement, his house was littered with garbage and drug paraphernalia -- including needles -- when police arrived.
Casey -- who currently sings for the punk band D.I. -- was immediately hospitalized nearby and survived. He was arrested soon after.
Casey was officially charged today -- with one count of child endangerment, and one count of being under the influence of heroin. He's currently being held on $120,000 bail.