Replying to Whiplash. To sue, or not to sue?

Ok, so on Thursday I was rear-ended. I stopped for a dog in the road (didn't even slam the brakes, just slowed down gently), but the guy behind me didn't see me and he smashed into me doing about 40mph. Not only is my car very near totaled, but I have a case of whiplash. I went to the doctor and got x-rays and stuff and was officially diagnosed with whiplash (along with being on painkillers and muscle relaxers out the ass). Should I sue the guy who hit me? A friend of mine got whiplash in an accident and got 7 grand for missing work because of his neck.