Well, it's hard work, but you knew that when you signed up! Frankly I find having a newborn, assuming no unusual issues, easier than late pregnancy (like you I get SPD really badly, plus lower back pain etc)
Yes, it's pretty life-changing, but.. you knew that too.
I had similar before I had DC1. The doom-mongers. Who seem to think that everyone else thinks that having a baby is a walk in the park. Um, no. Most people are not naive. They know it's going to be hard. They don't need people going on and on about it though trying to scare them.
What these people never mention with their scare stories are all the good parts which go a LONG way to balancing the tough times. And it gets better all the time - it is a bit of a shock to the system at first which is obviously expected, but with everything about parenting, every tough stage passes.
Personally I think with some people it's a bit of a superiority complex/power trip thing going on with dispensing all these stories. Most people's experiences are different to each others anyway so you don't know what you will get. Every baby is different too. Most births go fine even if they aren't always to plan - people only tell the horror stories after all.
DC1 was actually a nightmare baby. Spirited, hardcore colic, I had no previous experience of babies AT ALL (think I had held one for two minutes once in the previous 20 years) and nor had DH. She came early, fast and hit our life like a hand grenade. But you know what? It was never as horrific as the people at work liked to make out it was going to be. Sure, there were awful moments, and those are the ones people like to tell, but most of the time we just bumbled along and there were plenty, plenty of lovely moments in amongst the tough ones. The ones who tell the stories make it seem like your life will be comprised entirely of those awful moments. Unless something is seriously wrong with you or baby, I can promise you it won't be.
If it was that bad the human race would have died out years ago! You will cope, because you don't get any option and when you don't get any option you find new strength within yourself. Bet your colleagues never mentioned that either.. evidently they did cope really because they're still here now with their children!
Sometimes people do get depressed, but statistically most don't. And unlike when you get depressed at other times in your life, you have the midwife and then health visitor making regular visits. So long as they're half decent, you can tell them if you feel you're not coping.. crap ones are in a minority.
It's a challenge, especially on the sleep front, but a lovely rewarding one 
And as you say, it is very much a new chapter in your life in a good way!
Try to take what they say with a pinch of salt.. some people do genuinely get their kicks out of trying to scare new mothers. Even if what they say is true, there's so much to balance it out that they're not saying. Hang onto that!