They are designed to only wake you at the optimal time rather than when you are in a deep sleep.

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Many people use a float to wind down or to get over jet-lag -- as a deeply relaxing float has much in common with a deep sleep.

CNN: Floating to good health

It was not the best of facilities - my locker door was busted, the shallow pool was excessively chlorinated and there was nothing hot about the hot tub - but floating in a rooftop pool before getting on my flight capped off what was the most fun I have ever had in an airport and led to a deep, relaxed sleep on the plane.

BBC: Changi: The airport of your dreams

Now I have been teaching this for over seven years because I heard these words over 10 years ago in a yoga class that totally woke me up from a deep sleep of ignorance of what really is.

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