A lot of good advice has already been posted up. You will hardly never get out on time. You will see a lot of stuff that will definitely make you feel different. Your back will hate you for life. The starting wage is horrible. People most of the time do not appreciate the work you do. Bad weather always equals to a bad day at work. Despite all of these bad and negative sayings about EMS I still love it and want to do it. I'm pursing my Paramedic certificate and I could not be more happier than ever. Oh, and I have a way better paying job than my EMT work, but I love what I do with EMS more. It's not for everyone, for me helping people is the best feeling ever. EMS is one big family of brothers and sisters.
Good luck, keep us updated.