Hey all, sorry for the late update.
little fella is back to normal, fay was right and vet seems to think it was heating related.
Hes been kept off the heat chord since, and hes all good =)
i don't know how he got over-heated when all of the other little guys were fine - i guess he was just sitting on the floor right where the heat chord was running under the click-clack.
thanks for the help everyone!
Do you have any ventilation in the plastic tub? snakes arnt the smartest creatures around but they wont cook themsleves if given a choice. I would suggest gettting a thermometer to measure the temperatures inside the enclsousre if you believe this is the problem.