deep bathing
pp. Bathing with one's body immersed in the water from the neck down.
Bathing in giant tubs that allow you to fully immerse yourself provides "serenity for the body, mind and soul," says Carter Thomas, a designer for Kohler. "Deep bathing is more sensual; it engages all of the senses."
—Nora Underwood, “The wired bathroom,” The Globe and Mail, November 23, 2002
2002 (earliest)
Designers say people are spending more time in their bathrooms. They want bathrooms to reflect their lifestyles and serve as a place to forget the day's worries. "When you wake up, you immediately go into the bathroom," said local interior designer Claude Barron. "Because everything is in there, from the shower to the closet, people don't leave the bathroom until they're ready to grab a cup of coffee and walk out the door."

When they do get time to relax, people are infusing home spas, steam showers and deep bathing into their new oasis. They're moving away from whirlpools, single shower heads and plain lighting, home-interior experts say. Now they want multiple shower jets with massage features, mood lighting and deep tubs that resemble bathing pools.
—Christina Minor, “Homeowners placing more emphasis on bathroom comforts,” Cox News Service, September 23, 2002
A leisurely soak in a hot bath is one of life's small but enduring pleasures. It's a relaxing and comforting experience that can ease a worried mind and soothe a tired body. (Anti-bathists who live by a "showers-only" credo might want to skip over this part.) But there's just one problem: When you bathe in a regular sized tub, some part of your body is always sticking out of the water, which lessens the overall effect. This might explain the recent popularity of tubs that are much deeper than normal, which enables the bather to sink their full body into the water. This is the deep bathing experience and it appears to be a budding bathroom trend.