cholera, colic
痧 centers on acute internal illness with severe pain: cholera and colic, both involving intense abdominal distress.
痧 combines the sickness radical 疒 with 沙, which likely contributes the sound. The character is used in traditional Chinese medicine for cholera-like diseases.
The sickness enclosure 疒 wraps around 沙 (sand). Picture a painful, gritty feeling in the stomach like sand churning, causing cholera or colic.
For サ, imagine someone suffering from colic suddenly saying 'Sah!' in pain: Sah -> サ, and the sickness enclosure holds the sound inside.
gua sha (traditional Chinese healing method)