If you keep very still, there's one more surprise for you, as you float in your chamber. You don't really know if you're floating in water anymore, because you can't tell where your skin ends and the water or air begins. For all you know, you might be floating in outer space.
Once you've settled into your float, your brain shares a few secrets of its own with you too.
You've tried to see your hand in front of your face, but even at an inch away, it's too dark. You can only hear your own breathing, nothing else. Then you suddenly realize your brain craves sensory stimuli, but it can't get any while you are silently floating, without sight or sound or touch.
So, your brain goes on alert, and your senses sharpen.
You really notice that once you finish your float. After your float, colours are more vibrant. Your hearing is sharper. Your entire sensory apparatus becomes far more alive.
But your brain supplies its own colourful scenery inside your float chamber, too. About halfway through your float, you can see things in your mind's eye with brilliant clarity. You can mentally visualize with more intensity in a float tank than anywhere else that I know.