Severe TBI and lumbar puncture shows low pressure cerebrospinal fluid

My son suffered a diffuse axonal injury in August 2015. After being told he wasn't going to survive we were devastated ,but we didn't give up. After 13 days, he woke up from his deep coma. He was a 3 on the Glasgow coma scale when he was admitted to the ER. After 60 days in rehab and not much progress, we were told to bring him home to"wake up more". We really don't know what was meant by "more", but it has now been 14 months and all he is receiving is a few hours each week of PT, OT and speech. In the beginning when he had PT, he was taking steps on the parallel bars with the assistance of three people. Then the vomiting started. This is the problem that I am seeking any information anyone can provide. Six months after the injury, he had a baclofen pump implanted. Approximately 3-4 months later, every time we put him in his standing frame, he would vomit. This would start anywhere after 5 minutes to 60 minutes. It varies daily. This is making his recovery very difficult. We don't know if the baclofen pump is the cause, if he is dizzy, if there's an inner ear problem, etc. He has had every test and scan possible, all show nothing. A lumbar puncture shows low pressure csf, not high. Has anyone ever heard of this being a tbi symptom and what is the solution? Thanks!