Are these two words related? You decide for yourself after reading this posting.
In the Eastern traditions there is a catatonic deathlike state called Nirodha "meaning "prior to the arising of ignorance and volitional impulse."
Like deep Samadhi, Nirodha is a very high non-meditative meditative state. During Nirodha there is no time sense, heartbeat and metabolism are slow and practically cease so very little energy is burned, and body temperature drops well below normal. In fact this spiritual catatonia is so deathlike that there is the danger of being mistaken as dead and so buried alive. It is said that Nirodha is a precursor to Ego Death.
Nigredo in Western alchemy is the death-like withdrawl of the soul from the body.
"The Gnani (the Enlightened) continually enjoys uninterrupted, transcendental experience, keeping his inner attention always on the Source, in spite of the apparent existence of the ego, which the ignorant imagine to be real. This apparent ego is harmless; it is like the skeleton of a burnt rope--though it has form, it is of no use to tie anything with." Sri Ramana Maharshi