Q: iPhone 5 getting hot

I have had my iPhone5 for three days. Today I was walking in the mountains and wanted to make a picture. The camera App wouldn't work and the screen went black. After coming home the phone was very hot and "dead". After about 1 hour it cooled down and I tried to get it started again, but to no avail? I've had an iPhone 4 for three years and never ever experienced something like this. Somebody out there who has the same experience and what did you do?