In 2014, musician Greg Felton fell into a coma. Isolated from the world around him, his consciousness went on a free-wheeling journey; a cat-and-mouse entanglement with shadowy enemies, all played out entirely within his mind. Now happily recovered, Greg remembers every detail of this imagined story, and this play – adapted by Miriam Higgins from Greg's own writings – sets out to show us just what it's like inside a comatose mind.

Three actors collectively play Greg's consciousness and intellect, debating between themselves what's happening to him while playing out scenes from his imagined reality. There are some neat gimmicks here: a flipchart represents Greg's memories, highlighting how his dream-like story is often influenced by remembered concerns from the real world. All three performances are slick and energetic, with occasional quirky humour keeping the action moving along.

The programme notes take care to explain that Greg's experience wasn't like a dream; it was clearer and more intense than that, that say, as vivid as everyday reality. But what we see on stage is certainly dream-like, filled with logical gaps and outright non-sequiturs – such as the time when Greg enters a pub in Southampton and leaves it to discover he's in London. Events in the real world intrude into his inner story – some characters are recognisably doctors and nurses – and the narrative returns repeatedly to seemingly banal worries, like getting to Waterloo Station in time to catch a train. These are all characteristics we'll recognise from our own ordinary dreams, for all that those dreams are less vivid and memorable.

And I'm very sorry to say, I think that's a fundamental problem. Through her commendable desire to remain true to Greg's real experience, playwright Higgins has sacrificed most of the things which make a plot interesting: coherence, purpose, and above all a sense of peril. We know that Greg (thank goodness) lives to tell this tale, and we know that the dark forces he dreams about are all in his imagining. So, while it's intellectually interesting to see inside the mind of a coma patient, it's hard to feel emotionally invested in the story.

The final scenes – the slow process of waking up – are perhaps the most informative. Naively, I'd imagined that coming out of a coma was as instantaneous as waking from a dream; but as Higgins shows, for Greg, it was a gradual step-by-step reconnection with reality. The confusion he felt during this particular period is well-portrayed, as the three actors representing his consciousness share both excitement at their newly-rediscovered senses and doubt about what the signals they're receiving actually mean.

All in all, Dreamscape is neatly choreographed and dynamically performed, and does offer a convincing insight into a state of mind which most of us will never experience for ourselves. But I can't help feel there are other approaches – less literal treatments of Greg's story – which would deliver more of the structure and tension on which theatre usually depends. Dreamscape is an enlightening show, but not, for me, an entirely successful one.