I was never comfortable in bed, in any position.
Surrounded by pillows of all shapes and sizes was the only way I could fall asleep in bed. Even still it was a struggle. I needed a pillow between my knees, one behind my lower back, one tucked under my big belly, a couple for my neck and head. The quest for comfort was ridiculous. I bought three different body pillows over the course of my pregnancy.
However, in the tank I could lay down and rest at ease. I could float on my belly and feel no pressure, no pain, just a good stretch for my stiff lower back. I could float face up with no aching, no weight of the gigantic pregnant belly,no circulatory risk for the baby or myself, just comfort. I could lay on my sides without hurting my hips.