im so sorry you are having such scared feelings, certainly being a parent can feel like an awesome responsibility but most of us manage to shut that out.
I am wondering if, with two under the age of two (have I got that right?) you have some post natal depression. this isn't just something that lasts a few days after the birth, and can even start weeks or even months after the birth.
In addition, you have two very small children to look after, and that is very hard work and you may well feel under the weather from bad nights or overwork, the stress of it all or be a bit anemic? See your doc and get your haemaglobin levels checked and have a general check up to be safe, it is most unlikely you have anything seriously wrong and you will be reassured.
If you take the pill, depression can be a side effect and may just be felt as worry.
Try and meet other mothers and you will get some support from them
I do hope you feel better soon! Good luck to you!!