Does any one know why a stimson python would bite itself to death or at least appear to?

Have an autopsy to confirm, parasites such as mites and ticks may cause extreme irritation and the snake may have been desperate to remove them. Most likely the snake had some type of internal infection, bacterial or maybe viral, and in its later stages caused an itching, rubbing, or painful sensation and the snake's natural reaction would be to strike the external intruder. If there wasn't an external intruder such as live prey or another snake. An internal infection in its later stages is likely.