Re: why do we throw up when we have a concussion (or when we are drunk)

Let's see what happens when we are drunk. Alcohol  is metabolised very 
fast in our body into acetaldehyde and acetoacetic acid. During excess 
alcohol consumption, the levels of these compounds increases. Acetaldehyde 
being able to enter the brain, causes toxicity, and stimulates  specific 
centres in the brain for vomiting. These centres are the Chemoreceptor 
Trigger Zone in the medulla and the vomiting centre in the brain stem. 
Concussion is a temporary loss of consciousness without severe damage to 
the brain in a head injury. The injury causes changes in the balance of 
ions in the fluid surrounding the brain. This imbalance again affects the 
two areas mentioned above, and there is vomiting. Vomiting usually follows 
after a short period of unconnsciousness.
  For the concussion part, I think it is best you consult some one more 
experienced like an emergency medical expert before actually believing my 
answer. This is based on what I have read and accordingly figured out.