My mum had post-natal depression for quite a while after my younger brother was born and she had some not suite so nice treatments then got stuck on valium for years. It took her many years to gradually come off them. I hope the current drugs are not quite so hard to come off when you are feeling better.
Like said before, most people get depression from events in their life that have caused it, but others get it for no particular reason such as Alan and Fred. Obviously the first type is easier to treat as you know what has caused it, but does anyone know what causes the 'chemical imbalance' type?