Hi Danny,
I did exactly that a few months ago so if you need any support, post on here and I will try and help. Dropping citalopram in a week was hard going for me but GP wanted me on mirt as soon as he could and looking back it was worth it.
Hope it goes well for you....you should sleep really well with mirtazipine...I couldn't believe it the first night I took it, I slept for around 15 hours and still felt tired after that...but it does get better.
Jo.xx