How can he even charge me with a felony saying I hit him when he hit me?

I was in a rear end accident (I was rear ended) at a stop light. It was minor damage. I got out of my car and was immediately pepper sprayed by the other party. I got back into my car and drove to a dirt road, stopped and waited for a few (I was scared to death of what happened, who pepper sprays you for no reason especially when they hit you!). My eyes started burning really bad. I drove home (I lived maybe 15-20 minutes away). It burned like hell. I got home and immediately jumped in the shower to wash off. About 10 minutes after I get out, the police arrived at my house and asked me questions, etc. Why didn't I stay, what happened, etc. I was assaulted for no reason. I feared for my life at the time! My first priority in my mind at the time was to ease the burning (It felt like acid was thrown on my body!). Well the police put me in their cop car. They told me that the guy claimed I reversed into him and was threatening when I got out of my vehicle. They told me he wants to file a felony against me for assault with my vehicle when he hit me (again he is claiming I hit him in some form of road rage, I believe). I'm 6'2 and 230lbs so I could only guess my size scared him. Anyway, I was released immediately on Penal Code Section 849 In part (B 1). NO WITNESSES! Do I need to get a lawyer? Will my insurance take care of it? As far as I know, the police sided with him because I left the scene. I don’t understand any of this. They never gave me an incident report, only a certificate of release for detention.