What symptom did Hiroshi develop that indicated a more severe condition than a hangover?

The development of painful neck movement is a significant symptom that points towards a more severe underlying condition rather than just a typical hangover. This symptom can indicate meningitis or other serious neurological issues, as inflammation in the meninges or irritation of the spinal cord can lead to such discomfort.

A hangover typically presents with headaches, fatigue, and dehydration-related symptoms, none of which usually involve neurological signs such as painful neck movements. Therefore, while headaches are common and skin rashes or fever can have a variety of causes, the specific symptom of painful neck movement suggests a critical need for medical evaluation to rule out serious complications.