The Cruel Intentions star gave birth to her first son, Arthur, last July (11), but just weeks after his arrival Blair was jetting around the world to promote her movie Dark Horse.
She's now heading back to work in her new role as Charlie Sheen's therapist and love interest in his upcoming sitcom Anger Management - and she's mentally preparing herself for the challenge after a hectic 2011 left her struggling to cope.
Blair tells TV Week, ""Somehow I was just hanging on. But then it caught up with me - totally - and, since then, I've just fallen apart. I need to get myself back together so I can go back to work so I can pay for a house for this baby.""
However, the actress admits she's already exhausted because little Arthur is still not sleeping well.
She adds, ""I'm seriously sleep-deprived; I can barely put a word together. I have not functioned. I'd go to these 'Mommy & Me' classes and they'd be like, 'Oh, my God, my kid still wakes up twice a night or once a night,' and I'd just burst into tears, thinking, 'Oh, I wish! I wish my child woke up twice a night!'
""I'm definitely struggling right now, like so many mums who are trying to be as close to their child as they can and get back to work. It's such a common problem, but you feel like you're the only one in the world.
""It's (motherhood) one of the most horrendous things that's ever happened to me, as well as the most amazing.""