spawning?

I posted a message a while ago now about my fantail sitting on the bottom of
the tank most of the time. She is still doing this but the problem hasn't
got any worse and there are still no other signs of illness. She is eating,
she doesn't have clamped fins or any marks or blemishes and my water
parameters are great.
I had the day off work yesterday and spent a while watching the tank and it
seems that she and one of my males are showing signs of spawning behaviour
when she does decide to have a swim about. My question is, is this typical
behaviour of a fish heavy with eggs? She has become slightly larger around
the midriff than usual although not hugely so to make me consider dropsy or
something similar, If she is full of eggs it would certainly explain why she
isn't showing any other signs of illness than sitting on the bottom of the
tank. If it is eggs, how long would it generally be before she would spawn?
As I've never dealt with breeding goldfish I really have no idea about the
process involved so I could be clutching at straws here, but it would
certainly make sense.
Mel.