Sleeping your head into train oil

Does anyone know the origin of the phrase "Sleeping your head into train oil"?

For what it's worth I found the following but don't hold me to it as it sounds a bit far fetched but ya never know:

"Time to wake up-or you'll sleep your brains to train oil".

Train oil is whale oil.

"Train oil" comes from the Old High German for a droplet or tear, because the oil was originally extracted drop by drop by pressing the whale blubber.

The oil was burned as fuel and in the Eighteenth century, London's reputation as the best-lit city in Europe was partly the result of its easy access to train oil brought in by the whaling fleet based in the city's docks.

Whale oil was also used to make soap and for other purposes.

So the saying presumably contained the idea that sleeping too much turned one's brains to mush.