Harry Rock, from Eastbourne in East Sussex, was not suicidal and died through misadventure, coroner James Healy-Pratt ruled.
The teen, known as Bear, was academically advanced and preparing for his GCSEs, but wanted a six pack.
His mother Amanda Rock found him after a home tutoring session.
She had gone to check on him, and told Eastbourne Coroner’s Court: “I almost walked into him.
A dressing gown sash was caught around his face and under his chin.
The teen loved cats and gaming but his tutor, Rowanne Brown, did notice a bit of “teenage angst” over his study, and said he got “visibly upset” over being left out of a holiday which his dad and stepmother arranged with their other children.
However, a written statement from Harry’s GP confirmed there was “no mention of mental health issues” in his medical history and police found nothing on the student’s phone or social media indicating he was suicidal.
Ms Rock said: “I truly believe it was a horrific accident.
“He was fun, loving, caring – he’d always open the door for you. He was a gentleman, not loud, not lairy.”
The coroner said: “This was a tragic experiment that went very wrong, but it certainly wasn’t suicide.”
A fundraising page in Harry’s memory has raised more than £1,500 for Cats Protection and You Raise Me Up, a charity supporting families who have lost young adults.