Decisions - Is it too early to start making them?

Over the last few weeks, I've been thinking a lot about my personality and the way I act in certain situations. I'm writing a blog post about this because getting my thoughts down in writing seems like the easiest way to clarify them. I'm starting to think that I should stick with being a medical scientist and not continue on to being a doctor. Over-thinking things has always been a terrible habit of mine, and I don't know whether it's too soon to start thinking about something that's so far into the future, or if it's important to make these kind of decisions now. I know, I'll never truly know until I get there, but what if I do study Medicine for four years and then realise I'm not cut out for it when I begin my internship? I don't think I am emotionally strong enough to be a doctor, nor am I very good at making quick, accurate decisions in critical moments. I handle pressure well, but when it comes to making the right choices on the spot, I just crack. I don't think I could handle someone dying on me, I don't think I could handle not being able to help someone... I know I've said I want to specialise in pathology, which is okay, because those "patients" are either dead, or you're just working in the lab. But there's still the four years working in a hospital prior to specialising; that's what scares me. I know I'm still young, I have a lot to learn about life still and I am sure experience will make my emotional "intelligence" so to speak a lot stronger than it is now. But I still worry. I want to be a doctor, I have for years. There's nothing more I want to do with my life than to be a healer. I want to cure the ill, help those who need and rely on me. But maybe I'll have to do it in other ways, I might not be right for this career at all.