Mental break pending?

Hi, i really need some help. I think I'm on the verge of a mental break but i cant seem to stop it. I worry ALL the time, about everything, I'm so stressed i can't remember the last time i "switched off" or felt relaxed. I work part time and have 3 children who are my whole life, but after a few health scares i am TERRIFIED I'll lose one/all of them. I cry myself to sleep some nights just worrying something bad might happen and its making me so miserable that I'm starting to not enjoy our time because all i can do is worry, or feel sad about 'what if'. I cant bear it but i also cant stop it. Please, please, help me break this vicious cycle.