Hi,
It has been a long time since I started venlafaxine so I don't remember what problems I might have had when I started, but I second not forgetting a dose. I have really bad side effects if I forget a dose. They are worse since I am taking a higher dose now (400mg/day). I will feel dizzy, disorientated, depersonalize, and light headed. These will lead to it being hard for me to concentrate. Good luck with finding something that works.