One of the things you will hear over and over and over in beginning/intermediate/advanced acting classes is about "being in the moment". It sounds painfully obvious, but putting it into practice as a beginning actor, it's easier to say and harder to do. But you must do it if you want to really immerse yourself in the character you are bringing to life from the page. You yourself don't go around your daily life thinking about every thought that you have thought or will think later, every word you have or will speak, so why would your character do the same? If you do start thinking about all that stuff versus what you're supposed to be doing right then and there in the scene, your scene quickly goes off the deep end as you start focusing too much about where you're supposed to be on the stage, what your next line is, what your scene partner is doing, etc.
Luckily though, your teacher is there to stop the madness and help you regain where your focus should be for that specific moment in the scene. However, in dealing with cancer we don't have the luxury of some third party being present to hit a pause button while you and your family/friends go through the motions of dealing with the doctors, diagnosis, second opinions, insurance companies, meds, co-payments, treatments, and so forth. You quickly learn you have to become more aware of when things start to get too much and hit that pause button yourself to get back "in the moment." And it's totally acceptable to do so.
If the doctor is talking to fast and you can't remember what he said two sentences ago? Speak up! Ask him to repeat himself. It's also a good idea to bring someone along with you that can be there to hear things as well. If you can't have a close friend for family member be there, bring a notebook to write in, or pull out that smartphone and start typing down what you are being told. Mentally stay in the room with the doctor, and don't think about how what he is telling you is going to affect that trip you're taking in two weeks. What is he saying right now? That's where you're focus should be.
Ask questions; show that you've been listening. Don't just sit there and act like silent sponge. Take a second to process what you've been told, and then acknowledge it. Interaction is critical, and it shows the other person you care about what they are saying. That will make them care about what you have to say. Maybe, like the first time I had a craniotomy, it's a procedure that has to be done ASAP, and you'll be on the operating table within a week, regardless if there was something you had planned to do with some friends that weekend. Or perhaps, like my second craniotomy, it's a procedure that can be scheduled with your life in mind. Seeing Adele live was not something I was going to miss and since the second biopsy wasn't urgent, I was able to see her and then get a nice new two inch scar two days later. But the only way I knew that the second surgery could be held off was that I was mentally present in the room with my surgeon and my father, listening to my surgeon explain to me why the biopsy of the second tumor had to happen, and that it wasn't too urgent. If I had some plans, he could work with them. And thus I was able to coordinate with work about being off for post op recovery, finish out my current acting class, and see Adele at the Greek. And yes, she's amazing live.
There's only so much I can write about being in the moment. The best thing is to keep putting it into practice, as I'm reminded every time I do a scene in class. My partner and I will start our scene and for the two characters, there is no audience, it's just two people making discoveries about each other and reacting to them. If my partner and I are there with, and for, each other, my classmates get to watch that happen, versus watching two people reading words off a page to each other. It's the same being in the doctor's office. If you're both there in that room, it doesn't just feel like the doctor came in, read something off your chart with the hope you'll think about it later. You'll be thinking about it at that moment and respond to him or her right then.