iPhone 5 lose signal when playing intensive games

I was playing Modern Combat 4 and when i finished playing it. I returned to the home screen and saw NO SERVICE. So i had no signal . I had to wait 2 minuted and after it came back. it also gets very hot after playing some games. So my question is > Is this normal?? And why do i lose the signal when i'm playing an intensive game?

Already Thanks!! Sorry for my bad English!!