Darkroom retreats

[John]

Master Mantak Chia and also Jasmuheen seem to recommend (for those who are ready) Darkroom Retreats, where the participants spend at least 12 days and nights nonstop in pitchdark conditions. Apparently some Tibetans have done and recommended this before, amongst other things to develop the third eye. It would completely change brain chemistry, partially forever, so that one can get a higher level of consciousness.
Does anyone know more from other sources about this?