Oh yeah, I was on venlafaxine for years despite it not working really anymore but I was scared of and unable to bear the withdrawal syndrome. I think it is similar, also in symptoms including sweating, diarrhea, anhedonia etc., to moderate strength opioid withdrawal. Just that it takes longer, longest time I went were I believe 5 days, after that my tolerance was down from 300mg to ~75mg, meaning that 75mg were enough to keep the withdrawal away. It indeed takes just one day or half without taking the usual dose and withdrawal sets in.
My way out was to switch to fluoxetine with its week-long half life and thus integrated taper, and use Kratom against the remaining symptoms. Now I'm finally clean off any antidepressant for 2-3 months and while the first one was still hard due to nervousness and other PAWS stuff so do I now feel like before while on these 300mg's of venlafaxine.
For how long were you taking the effexor, and against what symptoms (depression, anxiety etc)?