Android controls completely disable themselves?

[TheTechnoToast]

I've had this issue a couple of times now, and would just like to know what's causing it. I was typing away in the YouTube app, and the phone screen lagged a little bit (as it does), but when it came back, I found that the touch screen became completely unresponsive, as did the keyboard and the buttons on the phone. I doubt it is a hardware issue, as I was able to reset the phone by long holding the power button. Once the phone was reset, I was able to use all the controls again. What's causing this? Thanks.