Problem with my Iphone constantly kicking me out and returning to my home screen

I recently traveled to Italy a couple weeks ago. During a layover in Frankfurt, I noticed my iPhone would kick me out of whatever app I was using and return me to the homescreen. Then it would ask if I wanted to shut down. I always hit cancel. It did this throughout the trip. When I returned, my phone was working fine until last night. It constantly kept flashing my homescreen over and over until before asking if I wanted to shut it down. At times, my phone would take pictures of my homescreen. Any ideas?