An afterlife would be terrifying for me

[Anomalocaris]

But the neuropsychiatric of contentedness in the demented is only inferred from outward neuromuscular behavior.     Is the loss of The capacity for inward concern and worry the same as contented?    In that case a rock or vegetable is contented.

I would think Real contentedness requires at least subconscious appreciation of possibility, presently unrealized, of disagreeable discontent.

Are you stating that psychiatrists assess the condition of the demented by their outward appearance?

Yes, rocks and vegetables are content, every bit as much as they are discontent.

I have no idea where you are going with your last statement. Sounds new age hippy.

Yes, I mean precisely that.    The ability to read minds is as yet denied them. 

So Just stopping all your biological functions will make you contented.