sickness, distress
瘼 centers on a state of suffering: physical sickness or mental distress. The two given meanings are closely linked as forms of affliction.
瘼 combines the sickness radical 疒 with 莫, which likely provides the sound. The character expresses illness or distress.
The sickness enclosure 疒 wraps around 莫, like a person trapped inside an illness. Picture someone confined by sickness and distress.
For バク, imagine a sick person backing away from their distress: back -> バク, and the sickness enclosure 疒 holds them back.