Definitely the Effexor, you are going through withdrawal symptoms, no matter how slowly you come off the med, you will get brain zaps and the spins. Your doctor is tapering you off too fast, it should be at least a week to ten days between drops.
Is this your regular doctor, or a psychiatrist? How long were you on the med for? If you've been on more then a couple of meds or they stop working, please get a referral to a psychaitrist, it could indicate that there needs to further investigation which a GP can't do. If Cymbalta is in capsule form you can split them up, so you have tapering off even more slowly. I did that with Cymbalta, down to a few grains and omg I still felt like hell. The quick switch should help though.
I think it could be your meds. I was on effexor and it's a hard med to come off of. Maybe your tapering too fast. Or it could be the effexor it's self. It made me extremely tired and I was on a much lower dose than your are. Feeling dizzy is probably from withdrawal. I went through that. The best thing to do is call or see your Dr. and ask about your symptoms. I hope you feel better soon. Remar