Horizontal Lines on iPhone?

It only happened for a few seconds, but while my phone was plugged in and playing music, all of a sudden horizontal lines showed up on the screen, as you would see on an old TV if it was on the "wrong" channel. This stopped when i pressed the power button, but i'm still worried. I tried to take a screenshot but it is just of my lock screen, even though it was taken with the lines showing.... Does anyone have any idea as to what could have caused this? I'm not going to be too worried as it could have been a one-time occurrence, but any answers or suggestions would be appreciated!