In 1954, John C. Lilly developed the isolation tank to test the effects of sensory deprivation. Such tanks are intended to completely deprive the brain of any external stimulation; they are lightless, soundproof, and filled with warm saltwater to promote flotation and reduce skin sensation. Isolation tanks are now used for meditation, relaxation, and in alternative medicine. A therapeutic session typically lasts an hour, and it is reportedly common to experience what during the first 40 minutes? Discuss