Floating on a warm bed of water, video screen overhead, Steven Fields, a 30-year-old airline reservation employe, was surrounded by darkness. He listened to the sound of his breathing, yielded to his daydreams and bathed in tranquility.

Fields took his turn in the coffin-like bathtub at the Bethesda Mental Health and Biofeedback Clinic, seeking a remedy for his fatigue and a better way of managing the stress in his life.

Upon emerging from the 200-gallon tank where his body was buoyed by 1,000 pounds of silky Epsom salts, Fields said, "it feels like what I would think amniotic fluid feels like . . . I almost felt like the tank was my head and I was the brain floating around."

The float tank has just been installed at the clinic by Dr. Louis Essers, a 42-year-old psychologist who has dubbed the tub the "Lesserstress" tank. Essers, who has been using techniques such as hypnosis and biofeedback to help people control unwanted behavior patterns, believes that floating in the tank may provide the optimal environment for relaxation and learning.

Essers' clients may come to the tank just to rest, or they can view videotapes that will attempt to teach them anything from improving their tennis stroke to learning not to overeat. Essers explains that when a person is very relaxed, his or her capacity for learning is improved. The tapes, which repeat some desired behavior, are a way of "reinforcing by modeling optimal performance." Essers said that he has been approached by a professional golfer and an opera singer who would like to use the float tank to improve their skills.

Essers said that over the years he has found that more than half of his psychotherapy patients "were experiencing extreme stress . . . (many) with physical manifestations." So Essers, and his wife Cheryl, who manages the practice, decided that time was right to invest $20,000 in the tank and requisite plumbing.

The idea of floating in a warm, dark tank was developed in 1954 by John C. Lilly, a National Institutes of Health researcher who found that for short periods of time, this sort of isolation produced the best kind of rest. Other scientists have shown that floating helps to reduce high blood pressure, chronic back pain, depression and hangovers. Essers is hoping to use the tank to treat women who suffer from premenstrual syndrome.

The Dallas Cowboys and Philadelphia Eagles of the National Football League and the Denver police department are floating their members for relaxation and sometimes use the video as a teaching tool, Essers said. He said that while many people find the notion of floating novel and fun, Essers says that he doesn't want to turn his practice into a health club and will be assessing the mental and medical needs of prospective patients.