Meeshy - I didn't feel sad as such, because I came to a realisation that the choices I had made in having a family, and the beliefs I had about the way I wanted them to be cared for, meant that I would never be able to reach the top of my career anyway.
So, for example, having made the decision to have children, I didn't feel that I wanted to hand them over 12/24 hours a day to a nanny, which is what I would have had to do to 'compete' with the blokes in my field who had full time wives doing all the childcare/ housekeeping.
Also I realised that my sense of priorities had changed - I was getting irritated by pointless travel to meetings (when a teleconference would have done) as it was taking me away from bedtime stories, or annoyed with last minute deadlines which ate into family weekends together.
If I had to describe my emotions at this time, they were more 'anger' and 'frustration' rather than sadness. For a while I was angry that no one had told me that having children would have such an impact of my time and career, and then I was angry and frustrated that my company was so inflexible about any REAL options to let me balance work/ home life. I also went through I stage of being angry with DH - for not earning enough money to let me do just one thing properly, either by paying for enough childcare, or supporting us totally if I just did the 'mum at home' thing. I was angry for all the usual "why do I have to do half the work and most of the household/ school stuff" reasons.
It's now a couple of years since I left, and in that time I've thrown myself partially into school/ PTA, as I thought that this is what part-time working mothers do. However I have to say I have found it massively unfulfilling ( - sorry!) so in September I'm going to be ploughing lots of time into the next stage development of my consultancy work, but still trying to be around for the kids from 4 pm most days.
It's a bit of a chick-lit read, but get hold of the novel "I don't know how she does it" - it's all about exactly these feelings, and it will make you laugh a lot if nothing else. That's if you can find time to read it, of course....