Complex sentence: That night, he is awoken by a sound like flapping sheets in a high wind and as he sits up in bed the sheets from the other bed across the room writhe and contort as they rise up into the phantom from the shore.
Split into simpler sentences: That night, he is awoken by a sound like flapping sheets. As he sits up in bed, the sheets from the other bed across the room move and then rise up into the phantom from the shore.