Shell shock, operational exhaustion, battle fatigue: choose an old name or a new one, the human cost remains the same. This one-man play follows a young British soldier – given the traditional Everyman name of Tommy Atkins –who's recently left the Army after six years of service, including harrowing tours of duty in the desert. He's enthusiastic for the future, keen to settle down with his girlfriend, naively certain that he'll walk straight into a job. He's chirpy and likeable. And he definitely doesn't have shell shock.

The narrative's delivered at speed, without even pausing between scenes, and while this has its downsides – there's no time for plot or character developments to settle in – it's highly effective in drawing us into Tommy's never-restful mind. He's suffering more than we first realise, perhaps more than he realises, and the cleverly-structured script gradually reveals a turmoil which presumably was there all the time. Harmless-seeming signals early on, like frustration with heavy traffic or a rant about IKEA, subtly morph into a less healthy, more disturbing sort of anger.

We witness the erosion of Tommy's self-image, too: at first he can't understand how anyone's ever late for work, but by the end he's wasting days at home sitting in front of the TV. But this is a well-rounded, multi-dimensional story, and the people close to Tommy have problems of their own – reminding us of something we know from our own lives, that crisis can flare unpredictably when pressures from outside crash up against upheaval within.

It's often said that actors deliver a "stunning performance", but in this case it's literally true: the intensity of Tom Page's portrayal is a shock for the senses, though to director Tim Marriot's credit it never feels out-of-control or over-done. The small stage seems barely enough to contain him, and as the story turns darker and Tommy's world closes in, Page subtly shifts from energetic enthusiasm to a portrayal of a man fretfully pacing a mental cage. Just two or three moments are slower and quieter, allowing Page to let potent and affecting emotion flow through.

I'm told that Shell Shock has toured military bases, and I wouldn't presume to comment on its impact for those affected by the troubles it portrays. As a straightforward piece of theatre, however – which is what I'm here to review – a couple of issues do stand out. The first is the painfully on-message advice about phoning Combat Stress, a charity set up help people like Tommy; for a general audience, this would be more convincing and effective if it were worked more subtly into the plot.

And my second concern, which is a nuanced one, surrounds the stereotypical squaddie attitudes which sometimes pop to the surface of the monologue. We're told at the beginning that we're Tommy's confessors – and he speaks directly to us, maintaining direct eye contact throughout. So there's a distracting sense of complicity when he uses words like "towel-head" – the feeling that I was being asked to endorse something I'd ordinarily frown at. This would be fine if it was meant to be challenging, but in this case I think it's just there for realism, and realistic things which send your audience's minds off on tangents are sometimes best left out.

But I realise that Shell Shock isn't quite meant for me; it's an invitation into a world I can never fully understand. So I'll give the last word to General Sir Mike Jackson, quoted on the front of the programme, who praised the "vivid and compassionate portrayal" of the ex-servicemember's life. He was writing about the book the script is based on – but thanks to Marriott's clever adaptation and Page's commanding performance, this stage version is vivid and compassionate, too.