wakeup...I know exactly how you feel; I 'd only just found out I was pregnant, was feeling awful, both physically and emotionally, and was terrified about what people would think. I'd stopped taking my ADs as well (didn't want to be hurting baby) and my mind was just mush.
But, I went to see the doctor, talked everything over with him and he agreed that my health was far more important than work. My DH than called work to explain what had been happening and they have been great about it tbh. I'm sure they are pissed off, but all my communication with them has been friendly and I get regular emails from colleagues chatting about things at work and asking how i am.
I think they know I won't be back as they sent me some stuff of mine that was found lurking in a drawer that would've waited if I was coming back in the next couple of weeks, but they haven't mentioned anything.
I think the depression can cloud our judgement and make us worry about things that perhaps aren't there, or that aren't as extreme as we think. And although your high flying boss seems to have it all; I'm pretty sure she can remember the more vulnerable side of being a parent and will be supportive.
I'm not sure about the HR side of things tbh. I was on holiday before my sick leave, so was on full pay for a bit, but am going down to SSP soon. Do you have any accrued holiday from your maternity leave? Could you maybe arrange to take this to give you a bit more breathing space? There are a few HR bods on here; maybe start a thread in Employment issues asking for advice? flowerybeanbag is very clued up on all this stuff.
All that aside, just remeber that you are the most important person in all of this, your family second and work comes in a very poor third. Getting yourself well is the number one priority!
Take care
daisy xx