Help? boyfriend in car accident...?

Okay about 2 weeks ago my boyfriend was in a car accident and got taken to the er and he complained of back,neck and wrist pain so the er took drays of all three places plus an MRI of head I think. They didnt find anything but a simple wrist sprain. Well, a few days later he overdosed on pain meds and got taken to er and then icu so ever since then he been in icu and drugged up and on a ventilator machine. Well yesterday they took him off the vent. And immediately he complained of pain in his right leg and neck and they have done ultrasounds, drays MRI and all and found nothing. What could his pain be from? Something they can't see...