I don’t think you’re silly. I don’t think you’re overreacting. I think you are sick. Please get yourself to a doctor right away. The symptoms you are reporting can be caused by quite a few medical conditions.
Being a substitute teacher is one of the hardest jobs in the world, it’s true. Being unable to find work and worrying about your future is certainly stressful. But before you write your feelings off as stress-related, you absolutely must get a thorough medical assessment. My guess is that you know there is something wrong and you haven’t wanted to face it. But the truth is this: If you do have a medical problem, it’s only going to get worse if you don’t get a diagnosis and treatment.
Do ask your husband to go with you to the appointment with your doctor. Feeling as you do, you need the support.
I certainly hope everything checks out fine. If it does, then make an appointment with a counselor to learn some stress reduction techniques. But if you are indeed ill, you’ll have taken the first step toward getting care.
I wish you well.