I get this feeling too and actively look for it. My best times achieving this have been scuba diving or snorkeling, sitting still after an intense ashtanga class, stopping by after a storm while driving out of a woodsy lonely area. That lack of auditory or otherwise sense stimuli makes me feel super calm but I try to watch out how I do it so I don’t freak myself or others out. I have been tempted to go to a flotarium, you know like that kid from Stranger things in her giant tub of water, but it kinda scares me.