Physics at play there:
F= ma
That large a mass, even at a slow acceleration delivered a massive force to his unprotected skull. Wouldn’t be surprised if he didn’t survive. At the least he’d likely have suffered spinal compression injuries, possible meningeal tearing, and if his skull was fractured the sudden intense intracranial pressure might well have resulted in an instantaneous uncal herniation*, and no one survives that without life-altering consequences, if they survive it at all.
Then again since the bucket was free to move he was perhaps not taking the full force as he would have if he was on a static platform (on the ground), which alleviates some of the worst of these described downsides…
*(Uncal herniation occurs when the pressure in the skull forces the brain matter down into the brainstem.The brainstem is a vital part of the brain, responsible for controlling essential bodily functions like breathing, heart rate, blood pressure, and the sleep-wake cycle. Prognosis is poor for even a short period of herniation).