Hopefully since the time you posted this, you have gotten this checked out. It could be something serious or just a plain infection. One shoud hang slightly lower than the other, that is normal, and one testicle should be slightly larger than the other as well. If one testicle is hanging much lower then I would call your doctor right away. Are you experiencing any pain, hardness of the testicle? Does your lower abdomen/kidney area hurt with a dull ache? It could be an infection that they treat with antibiotics, it could have been nothing, but it also could be somehting more serious. By now, I hope that you have gone to the doctor to have him check it out. It is not something fun, but hey it is your health and there is nothing more important than that.