Reducing your dose 10% a month to six weeks is the safest way to taper any psychotropic drug.

I have had a very similar experience with withdrawal as the one you describe: bad headaches, dizziness, disassociation, upper back pain, fatigue, irritation, etc. It is hell! I've been coming down from 112.5mg since the beginning of April, and about four months later, I am at 31mg. I didn't stick to the 10% rule, though. I wanted to go faster to feel like I was making progress because I hated what Effexor did to me in the first place--blunted motivation, took away emotions, destroyed hormone levels.

You should stabilize at your current dose, wait until the most acute of the withdrawal symptoms go away, and then decrease by 10% thus forth. Your doctor might not know you need to taper 10%. Mine was surprised that I was facing such awful withdrawal and so unwilling to just reduce by 37.5mg every two weeks (that would have killed me!).

I'm sorry I can't offer any advice to make withdrawal any better. If I knew how, I wouldn't have suffered as much as I have. I can only recommend going slowly and not pushing yourself too hard in anyway that might trigger a worsening of withdrawal symptoms.