my 3 yr old won't cry when hurt - WTH?

I wanted to offer up my experience with my natural son. At about 15 months I noticed he didnt cry when he snuck out of his crib and burnt himself five times in several extremely sensitive areas with the light bulb from the table lamp, and not a peep. In fact, id opened the door to check on him he came out smiling, as usual, and I notice a huge blister on his belly and arm. These were second degree burns. Not even dampened eyes. He was the happiest baby since day 1. He was very much loved, not neglected. I worked from home so no sitter. My husband was away in Iraq until our son was 2 and a half. This very happy baby who didnt feel pain flipped the coin at about 3 and a half. He became easily agitated, stopped listening, throwing fits. Complete 180. He was eventually diagnosed with broad spectrum autism NOS.