Your testicle(s) can recess into your abdomen. It's more common than you think among men. You should go get checked by a doctor as this is usually correlated with an increased risk of testicular cancer. In rare cases, it can become "stuck" behind muscle and tissue layers in your abdomen and cause pain. Sometimes there are simple, non-invasive procedures that can be done to correct the problem.
This is far more common in younger males with developing testes. So, if you're still fairly young or undergoing puberty, it may be completely normal and correct itself without issue. Still best to be safe and have a doc take a look. Also, if it happens in the future (once you've cleared it with a doc), and if it's not too far in, try to *gently* massage it back down into your scrotum yourself. This will help it correct itself naturally through development and help to prevent it becoming permanently recessed.
As long as you have one functioning, you shouldn't have problems with sperm production or hormone balance.
ADD - PS: sorry you're catching so much crap over this question. I guess anything about balls brings out the trolls. It's normal, you're not weird, and it'll be just fine...