You are correct about the things you mentioned; 'cross addiction' is quite common, although some addictions like opiates in particular are 'dead ends' because people rarely leave them for something else. Yes, fiorinal contains butalbital, a barbiturate, and yes, rebound headaches are very common and probably part of your condition.
As for withdrawal, barbiturates, benzos, and alcohol all bind to subunits of the same receptor in the brain, and so they all are 'cross-tolerant' and the withdrawal from all is similar, namely the 'DTs' or delirium tremens. This is a potential fatal condition that includes seizures, but includes delirium, hallucinations, and autonomic dysfunction (changes in blood pressure and heart rate, for example). Given the danger of a taper out of the hospital I must recommend that you see a doctor to help you either in or out of the hospital. The safest way would be to put you on anticonvulsants-- valproic acid, or maybe a long-lasting barbiturate or benzo-- and taper that down. The problem, as you know, with tapering your drug of choice is that if you had the power to taper it, you probably wouldn't be where you are today! Most people start a taper, get into it, and then lose control and raise the dose again.
Do it right-- get a good doc, and try your best to be honest about your situation. If you can be honest and follow the instructions of those who can help you, things can work out OK. The problem is that we all have a tendency to treat ourselves, thinking only we can understand our problems. I wish you the best.
For some reason the forum won't allow me to post a new question, and I nee a doc to help me! have been addicted to hydrocodone for 11 months. I do realize that there is a deference between physical dependance and addiction,I am 16 weeks pregnant and terrified to tell my OB. I started at 3 or 4 500mg's a day and after my tolerance increased, the doc increased, the dosage and switched to lortab 1000mg, and I can 10-15 a day now. HELP!!! Oh I am 25 year old stay at home mom of three boys, and hubby works 80-100hrs.a week! I live in VA. and ALL my family is in MO! So no help with the kids!! I have to do something! PLEASE HELP!! I don't want this on my medical record, and my balance with my chronic pain management doc is outstanding, so I can't get a refill!