The mind is a firecracker, sparking and popping and bubbling. Then again does it really disturb you? If it does then I recommend several doses of hard liquor every day, to eliminate all thoughts and memories permanently.
Actually, the subconcious mind is constantly recording more than what your concious mind is focusing on. Perhaps an image set off a chain of mental events relating to different memories, yet only certain thoughts reached your concious mind. Just a guess you can play with.