My advice would be simple: Try to take a few days off if at all possible so you can go into this with a clear mind. Then for each of your possible choices think about:
* What does a successful outcome look like here?
* What does failure look like here?
* Is there an in-between outcome?
* How do you feel about ending up in each of these cases?
* What is the likelihood of each of these cases?
* If you go all in on this and fail, what realistic backups do you have? Does this change your opinion on the previous questions?
Take however long you need to choose, then act decisively and look back as little as possible.
I will also say that your expectations of a PhD in medicine being way easier seems off to me, but I am clueless about both medicine and machine learning, so what do I know. Do make sure though that you are making your decision based on good information.