Firstly, No one here can diagnose you, even if you had offered some real information. But to answer your question, yes, an injury can seemingly come out of nowhere. A (relatively inactive) friend of mine felt a soreness in his back after playing sports. He wasn't sure what it was, but it didn't cause him any serious problems so he let it be. 2 weeks ago he tried to stretch his back, and suddenly felt an almighty pain which completely immobilised him. I took him to the hospital where he was diagnosed with a C2 herniation of the spine. So yes, a seemingly healthy body can hide a serious problem. Go to a doctor if you're concerned. He will perform some simple (non-invasive) tests to find out if anything's wrong.