I can't say exactly why it happens but your symptoms are pretty common. I've never tried to go without for more than a day at a time. Does anyone know whether these or other symptoms are permanent? I have heard stopping SSRIs can lead to a long term SSRI withdrawal syndrome that can last years or longer, but I can't say for certain whether this is true of this drug or even SSRIs in general. I am currently taking Effexor and Prozac, and I'm scared to death that the side effects will never go away. I have been able to mitigate some of the sexual side effects with aromatase inhibitors like zinc and resveratrol, but I am still not 100% to where I was before I started. On top of that, I have never really noticed any benefit to my depression, my doctor was supposed to phase me off the Effexor and on to the Prozac, but he never followed through, this was at least a year ago. Now I'm afraid to stop taking either, but I also worry that the longer I'm on them the more difficult it will be to return to normal once I do decide to stop, or if I have to stop at some point.