<p>Research on health inequality has traditionally focused on metrics such as years of life lost and disability-adjusted life years. This paper argues that current metrics systematically undervalue health conditions causing extreme pain to patients. Cluster headache, possibly the most painful condition known to medicine, offers a striking example of vast misallocation of economic resources relative to the burden caused, particularly relative to resources spent on similarly prevalent conditions such as multiple sclerosis. This inequality is further exacerbated when considering the possibility that the most extreme human experiences may be orders of magnitude more intense than mild ones, significantly increasing the urgency of addressing conditions involving extreme pain in any economy focused on wellbeing. To better grasp the scale of the suffering caused by cluster headache, statistical data from the medical literature was aggregated into a publicly available suite of numerical simulations that estimate the global burden of cluster headache pain. Results indicate that adults with cluster headache spend 3.1 million person-days per year globally, experiencing extreme pain (rated as ≥9/10). The burden of cluster headache pain is compared to that of multiple sclerosis. An analysis of the research investment that has gone into both conditions in recent decades in the UK also reveals substantial discrepancies. Global under-funding of cluster headache may be even larger than in the UK data analysed in detail. Optimistically, it is estimated that a modest investment to provide universal access to existing treatments and to explore promising treatments could significantly reduce the burden of extreme pain caused by this devastating condition, presenting a remarkably cost-effective intervention for any well-being economy. Modest and ambitious improvements in healthcare metrics are suggested to aid the correction of such dramatic wellbeing inequalities in other conditions.</p>