Five Finger Death Punch Singer -- Wife and Sister Plead ... Get to Rehab, STAT!

Five Finger Death Punch singer Ivan Moody is running out of time -- his estranged wife says he's having bizarre Jekyll & Hyde-like episodes and needs to get help for alcohol abuse, stat.

Moody's estranged wife, Holly Smith, filed an affidavit with the Adams County Court in Colorado ... saying Ivan can no longer tell the difference between his real persona and his onstage one ... thanks to his alcohol abuse.

In the docs, Smith says Ivan's taking on the personality of the band's song, "Jekyll and Hyde." She says, "Ivan has talked to me in third person in a voice different from his own as if he were a demonic presence inhabiting a body."

Ivan's sister, Sandra Dykes, filed an affidavit of her own as well backing up many of Holly's claims.

Holly and Sandra think he needs to get into rehab immediately. In the meantime, the judge granted Holly a restraining order against Ivan after she showed photos of bruises he allegedly gave her.