Online scams can be difficult to undo, but not impossible. A lot may depend on how you transferred the money to them. If you used a credit card or a bank, you may be able to contact the fraud department there for help. A lawyer can help by attempting to locate the operators of the scam.
To answer your first question, some people who suffer a TBI or traumatic brain injury experience symptoms that can be helped by treating with a psychiatrist. To answer your second question, it is possible to sue the owner and/or driver of the car that hit you and seek damages for all your injuries. Whether that lawsuit would be successful depends on the facts of your particular case. You should contact a local lawyer to make sure your legal rights are protected.