Iphone 4s in pocket suddenly heat up

Hi all

My 2 year old iPhone suddenly heat up quite badly when it was simply sitting in my pocket. I quickly took the phone out and notice that the battery has dropped from 70 something per cent to 9 per cent, and it was in camera mode?

Scared, I just turned the phone off.

My phone battery has a really short life and I have to recharge around 2 times a day.

How my question is:

1) would the phone release excessive amount of radiation that it would affect my well being (it is on my right pocket of my pants)?

2) would it be safe for me to use the phone again?

Thanks in advance?