Answer:
Large as a mountain, small as a pea, Endlessly swimming in a water-less sea.
This is in a realm of true and in a realm false, but you experience me as you turn and toss.
Salty water everywhere but not sea in sight.
I make you weak at the worst of all times. I keep you safe, I keep you fine. I make your hands sweat. And your heart grow cold. I visit the weak, but seldom the bold.
I'm sometimes white and always wrong. I can break a heart and hurt the strong. I can build love or tear it down. I can make a smile or bring a frown.
I touch the Earth, I touch the sky, but if I touch you, you’ll likely die. What am I?