Reassurance welcome please!!!

[bookletters]

Sorry to be a pain but I need reassurance please.
Following the instructions of the doc I have been reducing citalopram from 40 to 20 for two weeks (and starting venlafaxin 37.5). This went fine and venlafaxin helped me massively immediately (sleeping, eating, starting doing things again, socializing etc).
Then on Monday I started taking citalopram 20 one day, nothing the next, then 20 again, nothing the next.
Today, I am feeling anxiety, low, worried, needy. I tried busy and this helped but since falling asleep earlier keep worrying I am going to be worse, have a relapse... I am starting to feel stressed about having guests tomorrow although I was really looking forward to it....
Has it ever happened to any of you?
Do you think it is caused by the citalopram withdrawal?
I am freaked out having gone from 2 weeks of massive improvement to today of feeling bad again :s