Quote:
As mentioned, at first you’ll likely find it difficult to remain in your dream upon becoming lucid. If the world around you suddenly starts to fade, or you inexplicably sense that your dream is ending, or you even feel that your dream consciousness is thinning, there is a technique you can try to salvage your dream: dream spinning. Dream spinning is extremely simple and consists of you spinning on the spot like you would have as a child. That may sound very silly, but the technique is extremely reliable. When you stop spinning you’ll likely find that the dream clarity has returned, and perhaps your surroundings will have changed as well. In fact, if you focus on changing the setting into something else while spinning, it is very likely you will find yourself in your desired environment after you stop spinning. Note that since it is likely your dream will completely change upon completion of dream spinning, you may lose lucidity. Thus, it may be wise to also remind yourself that you are dreaming while spinning. Also, verbal commands can be beneficial when trying to prevent your dream from ending. Of course dream spinning and verbal commands are tools for controlling your dreams, which we’ll get into next.
I took that from the FAQ... dream spinning. As for all I know just some random guy just said that spinning in your dreams is a way to maintain your clarity. That sentiment spread because no one contested him and some people tried it and it worked for them.