I am 73 years old
and have been on anti depressants for 20+ years,
and Venlafaxine twice. Once for 5 years, but I was silly and stopped it cold turkey. I was fine after 2 weeks, but depression came back after 1 year. So I went back on it again for 4 years, and as I say, have just withdrawn from it. This time, because I did it really, really slowly, I have been fine. I think your problem is you withdrew too fast.