Rachel Bagshaw has Complex Regional Pain Syndrome. She feels pain with no cause, almost constantly. It’s hard to imagine, and harder to communicate. Which is precisely what this show, co-written with Chris Thorpe, tries to do.

That’s a practical necessity and a philosophical impossibility. Pain is ineffable: it defies description. We don’t have the words for it – not exactly. That’s triply true for Bagshaw. Pain is her normal, part of who she is. She dreams in pain. Talking about it only serves to increase it.

That’s why Hannah McPake performs on her behalf. Stood in front of a curved metal gauze, she tries to find the words: hot suns under her palms; red, rectangles of rawness; a sensation that wants to expand into space.

The way McPake describes it, Bagshaw’s pain splits her consciousness. She talks of leaving her body, detaching or even dissociating. This show gives us a similar sensation. Melanie Wilson’s ambient sound and Joshua Pharo’s hypnotic projections combine brilliantly. One works on your body; ever skin cell vibrates. The other lets your mind drift, utterly entrancing. It’s an extraordinary sensation – an altered state. You’re not sure what’s real and what’s not.

Bagshawe’s story centres on a relationship: a lover who knew, instinctively, perhaps even telepathically, how she hurt. That’s love, she reckons; empathy without speaking. Only invisible attention feels like inattention – another paradox. How to speak about something that hurts to speak about? How to care when care causes pain? Theatre’s been called an empathy machine. The Shape of The Pain tests its very limits. Searing stuff.