I Have Taken Prozac 40 Mg For 5 Years. I

I have taken Prozac 40 mg for 5 years. I weaned myself off gradually of it 3 months ago and had no problems. I have been feeling very depressed recently and at the advice of my therapist, started back on it. I began feeling better within a few days, expecting to not feel any difference for weeks. Is it possible my brain "remembers" the drug?