Health Insurance Question?

I was wondering if I were to get on a health insurance now would it help lower my hospital bill? it is a little over $4,000 and i have another $300 for the x-rays and CT scans. I am a healthy person and could not really afford health insurance at the time and now i have gotten very sick one day and had to go to the emergency room. Would medicaid help cover this even though i already got the bill? thanks!