Rolling in the Deep is what a ship far out at sea does - in old fashioned, poetic language. The image is a small ship tossed on a very deep, dark ocean. At the beginning of this song by Adele, the singer says "Finally, I can see you crystal clear. Go ahead and sell me out and I'll lay your ship bare." starting a nautical illusion. Later on she says "Think of me in the depths of your despair. Making a home down there, as mine sure won't be shared." The lyrics conjure up an an image of someone alone in a deep sea of despair like a lonely ship rolling in the waves of the deep ocean - Rolling in the Deep

It could mean to love deeply or to be feeling pain cause by rejection. Either way these feelings take you to a new understanding of your emotions.