I honestly don't think he suffered as he died, and he died very quickly. It takes a long time to asphyxiate compared to passing out from blood loss to the brain. (It only takes 8 seconds in a sleeper hold to pass out) The weasing was probably involuntary muscles on auto-pilot until they inevitably lost the electrical support of the oxygen that was no longer being delivered anywhere.

He probably just blacked out and the internals shut down while the lights were out.