http://www.shiningworld.com/site/files/pdfs/publications/transcriptions/Mandukya_Upanishad_and_Karika.pdf
some technical details --
Visva - Waker in the waking state
Taijasa - Dreamer in the dream state
PrÄjƱa - Deep sleeper in deep sleep state
Turiyam - That which underlies the three states of waking, dreaming and deep sleep.