2001 Ford Focus my interior and exterior lights dim in conjunction with my rpm's revving like crazy.?

Also, if I'm slowing down, the rpms will drop hard. I was sitting at a red light and my transmission seemed to thunk. This is all happening at the same time. It doesn't happen every single time I drive my car just often enough that it scares me. Doing 60 on the highway last week my rpms went up to almost 7000. Any ideas anyone? Thanks for all of your help.