Starting the day with Panic Attack

I am a nanny, and woke up this morning with my regular routine and while one child (6 years old) was playing, all of a sudden I felt like I couldn't breathe and something was stuck in my chest, which only makes me freak more. I went to my room to lie down, explained what was happening to little girl and she laid there with me and praticed my breathing. Now I just want to cry and go back to sleep. How do you just carry on some days?? I've struggled with major depressive disorder for a while and some days you just can't operate. But what do you do when you have to work, or you are in charge of caring for someone else. Feeding them, playing with them, cleaning up after them and then you look at the clock and it's only 11 am!