Thank you very much for your responses, Jo*mar and Skeezyks!
Based on your responses, I should add a few important details:
1) My injury (concussion) has some components of hidden injury/pain, because as I start to recover I can do things in small, limited cases. So if people see me at the best hour of my day and assume I am like that all day, they not realize the extent of my injury (besides the hat, dark sunglasses, and ear plugs and headphones I need to block out things.) A ct scan or EEG doesn't show the symptoms. A DTI, fmri, or qEEAG would, but I doubt the WC would order an expensive test like that, and none of the treating doctors I've seen have talked about them (my mom read about them in an excellent book by Dr. Diane Stoler)
2) several people saw my accident
3) I don't expect any long-term costs beyond the few months of missed pay and handful of neurologist visits. Which is why I'm hesitant to get a lawyer involved. The reimbursements I am missing from WC is under 1k, not nothing, but probably not worth getting a lawyer for. Once I've recovered more, I feel confident enough bugging them myself for it.
4) So really, the main thing I am curious about is whether I should do anything before the IME to prepare for whatever may come after it.
Thanks again for your help. I've been wanting to ask these questions for several weeks - today was the first day where I felt well enough to post!