iPhone 5S Closing Out Programs Unexpectedly

[CyberCharon]

Quick question about the iPhone 5S - I've had mine almost 2 years and it has this habit of sometimes closing out my Google window without error message of any sort. I'll be playing a Youtube video and halfway through it will just close out. It doesn't do this every time but when it does happen, it often keeps happening for a little bit. Has anyone experienced a similar issue? If so, any idea what could be causing this and, just as importantly, how I can fix it?