I am currently on my second round of quitting caffeine. The first time through, eleven years ago, was brutal. I experienced severe headaches, I could barely move for three days. Keep in mind I had a very strong addiction (>3000mg/day). I never once threw up. You may have something else going on there.
This time around is much better. I was only at about 150mg per day. I experienced minor headache on my first day without caffeine, so I took a small amount of Pepsi and drank that. Next day I had no withdrawal symptoms. I was sluggish for the first week, but after that I now seem to be back to my normal energy levels. One side note: smoking pot seems to put me to sleep a lot quicker than it would have even at 150mg/day.
