Sometimes when i sneeze, my right arm with hurt pretty bad for 10-30 seconds. what could this be?

C/w ReferredPainFrom: mediastinum (& other possibilities). Embryologically, the heart, lungs & diaphragm begin formation in what becomes neck, adjacent to cervical nerves: 3,4&5. Thus these spinal nerves branches primarily relay brain controls which run through spinal cord (not all do, some via Vagus nerve, etc.) to these organs, Yet most C-3,4&5 nerves extend to arm bud which becomes the arm: Thus the connection.

Nerve: It is likely that the muscular effort involved in a sudden sneeze causes some compression of a nerve or nerve root in your neck causing radiation of pain down the arm. The compression may actually come from a disc in your neck. Since you don't have arm or neck pain on a chronic basis, there may be no need to do any investigation unless more symptoms appear.