I do this thing in the bath, I plug my nose and curl up under water, on my back and my knees to my chest, so I don't float to the top. I recently discovered I can cover my eyes so light doesn't shine through my lids. It's like sensory deprivation. I don't strain too much--well, sometimes I do, but not these days--and sometimes I curl into the fetal position. I don't ever feel any kind of spiritual womb rebirthing thing, but for a few moments after I resurface, my mind is clear as my senses adjust once again to the stimulation they so love/hate/never don't have. And as my mind is never clear, that's pretty nice.
"I woke in bits, like all children, piecemeal over the years. I discovered myself and the world, and forgot them, and discovered them again. I woke at intervals until... the intervals of waking tipped the scales, and I was more often awake than not. I noticed this process of waking, and predicted with terrifying logic that one of these years not far away I would be awake continuously and never slip back, and never be free of myself again." (Annie Dillard, An American Childhood)