When I feel bad about my performance, I try to look at my past achievements. I used to just do projects and disconnect once they had completed. Now, I have a small archive of pieces of code I can look at where I feel I genuinely improved as a programmer or had an 'aha' moment.
Recall, the intersection of technology and medicine fields is not simple. Both fields are expanding and adapting on a daily basis. The amount of expertise required just to hone a single skill (potentially extinct!) is a lifetime's achievement. Do you really believe you have already peaked and this is it? Believe me, there is so much more to come! Maybe you're not the all-knowing-expert-guru, but aren't you aspiring to reach that point?
Just relax. You'll be fine. Even if they found out, and it turns out you were an impostor, do you really believe you're going to get fired? You're already trained and in the field. You're being an impostor of what you're actually doing on a daily basis? Seems ridiculous.