Why do I keep having nightmares? HELP?

Two years ago I was in a car accident where the entire door was smashed in. I was making a left at night The lady didn't have her lights on. All I remember is waking up and not knowing where I was. Then I saw a bunch of commotion to the left. I tried to get up and I felt a pain like I never felt before from the chest down. I was afraid to look down cause once I focused I saw that there was blood on my window. I didn't sleep much for weeks after and thought they were in the room waiting (there was a guy yelling in my face right after. Some Hispanic guys that were following behind her, no racist comments plz) but I thought that he was in my closet. Spanish class was the WORST after that (once again no racist comments). Now, two years later, I'll fall asleep and have nightmares. Even yesterday I fell asleep in group therapy and woke up yelling cause I thought I was in it again. my knee was bent inwards. It's always haunted me. What can I do? Therapy doesn't help!!