Don't panic buddy. It might be that your smaller testicle has atrophied and stopped working from testicular torsion or some other injury or disease. But if that happened, you'll still be a fully fertile and sexually functioning man since all us guys have twin testicles and nature gave us all a spare nut just in case we lose one to injury or disease. My Dr.s said the remaining healthy testicle is designed to do the work of two testicles if one is lost or damaged. It can take months for the healthy nut to grow bigger and do all of the work of two nuts. Your healthy testicle probably already is doing the work of two testicles and looks even bigger next to your shrunk down testicle. Dr.s don't need to remove a small atrophied testicle as it is not doing any harm at all to you. It can stay in you as long as you live with no problems. Dr.s can test your testosterone and male hormone levels with simple blood sample tests to see if your male hormone levels are within the wide normal range. You can have a semen test done, by masturbating to ejaculation into a lab jar, and lab techs examine your semen to see if you are making normal amounts of sperm. My Dr.s say as long as I can make enough sperm and male hormones, one testicle is all I need to have kids and enjoy endless sex like every man with two balls. Good luck and don't worry, lots of us guys have only one testicle with no troubles.