I had to have surgery to fix the TMJ I had.
It started out like the OP's situation. I was doing something, heard a pop, and felt like my jaw wasn't sitting correctly. After a while, things went back to normal.
Kept happening, and it only got worse. Eventually, I couldn't open my jaw without it popping, and even more it eventually got to where i couldn't open my jaw without it popping very painfully.
Between your skull (T-temporal) and your jaw (M-mandible) is a cartildge Disc (J-joint) and these three things make up your TMJ. If that disc gets out of place, it will reak havoc on your jaw movement. That disc is tied to a tendon and as you pop it, it will cause pain in the disc, and will also aggrivate the tendon as the popping and pressure causes you to stretch, yank on, and irritate that tendon. As you mess with that tendon, it only gets weaker and stretches, which allows the disc more slack to move around in your TMJ. The more it can move around, the more likely it will fall out of place.
Eventually, the tendon will strech enough that the disc will no longer sit in its correct spot,but will actually slide forward and block your jaw from opening!!!
Go to a doctor, stat. It's only going to get worse and more frustrating
Do you have health insurance? There is a quick procedure to clean out your tmj, inject some steroids, and tighten things up. Out of pocket would be $1,500+ for the surgery, but its usually covered by health insurance (as was mine).
Having the procedure immediately corrected my problem. A few weeks later my jaw popped, but from something completely different. I opened my mouth really wide. Went and saw the surgeon, and he asked me to open my mouth till the point that it would pop. I did, he took a measurement, and he told me the average and healthy distance to open your mouth is about 38mm.. I had opened mine to 50mm when it popped. He laughed and said there's nothing wrong with my jaw, but that I was simply over extending it.
Basically I said
"it hurts when I do this"
He says
"then don't do that"