Hi Boy,
I have been through this fear more than once too. I would get periods where one testicle would ache for days and sometimes weeks, too painful to touch infact! It used to eventually go but the same thing could happen with the other one too. I decided to try and wear some more supportive underwear and don't seem to have the problem since or at least not to the same degree. I check them now and again and they seem to feel realtively normal. I did work myself up into quite a state about it at the time so I understand your concern.
Mark