I too seem to be suffering from some of the more 'scary' side effects. I took it for two months then started just taking the pills occasionally when i felt tempted to have a cig. Big mistake. The last month or so (3 months after starting) I'm having some serious mental health issues. Paranoia, short short temper, Depression, Panic attacks and loss of memory. Any one of these would be bad enough but having combinations of all them is really scary (Paranoia and memory loss is really bad together).
I went to the docs today as I'm at the end of my tether and he told me coming off/taking random doses of champix/chantix is the most probable cause. I knew my head was getting messed up so i stopped taking the tabs two weeks ago, hoping it was champix causing it. Things have been absolute hell since then. For the last two days i've taken one tab a day at the same time of day. Now almost human. Doc has recommended i continue for at least a week or two at this dose and come off them very slowly. lowerin to half a tab a day for week or so, then half a tab every other day for another week.
I can totally see the logic in this (Wish I had earlier!). Champix messes with brain chemistry. Suddenly stopping is not going to give enough time for things to rebalance in your brain, resulting in problems.
I was getting really worried It was me just losing my mental facalties, but I'm actually getting some comfort knowing other people are experiencing similiar things and I know what kind of things to look out for in my own behaviour now and can hopefully try to prevent spiralling out of control. If you know someone taking champix please let them know of the possibilities of physcological problems so they are at least aware to watch out for danger signs like mood swings, withdrawal from people, short temper, anger.
Also remember it does seem to be a minority of people having these problems
I really feel for the poor people that didn't discover these potential problems until too late. So please pass it on, talk to your partner/friend/collegue taking champix and let them know about this, They maybe be suffering in silence.