YES he could have gotten a concussion. I clicked on your question and first thing I thought just reading your title was concussion. Possibly - he has the flu or what-ever and it's coincidental that he fell out of bed same time he has the flu. But I wouldn't risk it. Do you know where he hit when he hit the floor? His head? Maybe he landed on a hard toy right at his abdomen? If he can't keep any food down, then there is a major problem.
Not sure if the doctor can take care of this at the office. He may recommend you go to the ER. My 1 yr old nephew had similar symptoms your son did (fell, was throwing up), they went to the ER. Don't remember what tests they ran and all, but they were there a while.
Good luck to you! Update us when you get a chance!