Bedlam by Christopher Brookmyre
HEAVEN IS A PRISON. HELL IS A PLAYGROUND.
Ross Baker is an overworked scientist developing medical technology for corporate giant Neurosphere, but he'd rather be playing computer games than dealing with his nightmare boss or slacker co-workers.
He volunteers as a test candidate for the new tech - anything to get out of the office for a few hours. But when he emerges from the scanner he discovers he's not only escaped the office, but possibly escaped real life for good. He's trapped in Starfire - a video game he played as a child - with no explanation, no backup and, most terrifyingly, no way out.