I don't think anyone here is downplaying the seriousness of the situation, but that the OP is of an age where she needs to learn to tackle these situations by herself. She is physically and mentally able of addressing the situation, so it's not appropriate for a parent to step in. It is emotionally difficult but it's something that everyone needs to learn..
Of course it is. But some of the posts here seem to be a little harsher than necessary in order to help this 23 year old learn that. She's still young and learning. We can guide her here and help her.
Also, we have to remember that the OP has a serious medical condition. That makes it much more difficult to "tackle these situations" or even learn to tackle them. It isn't so simple as being an adult who is and should be responsible for herself, who is both mentally and physically capable of addressing the situation. Yes, she needs to learn how to do this, but the difficulties are much more than just emotional when you have a serious, chronic medical condition.
I am speaking here as someone who has several chronic illnesses for many years and has had to deal with getting appropriate time off, etc. Sometimes I have navigated such problems more successfully than other times, I will admit, but you don't exactly get a handbook along with your diagnosis of disorder xyz about exactly how to solve the social problems it causes.
You just need to do the best you can, is what it comes down to for me. Did the OP's father overreact? I think if he had intervened strictly on the basis of getting time off, it might have been an overreaction. But he was reacting to the fact that his daughter almost died. I think any parent, regardless of the age of the offspring, would have a strong reaction to that even if they didn't do what the OP's dad did.
And sometimes, in such situations that involve serious chronic illnesses, you actually need the help of someone else, be it a parent, a spouse, a sibling, whatever, to help you handle work problems, etc. It's unfortunate but I have found it to be true-such as when I cannot physically call my workplace to tell them I am sick, even on the way to the ER, and I ask a relative to do it. If the father overreacted in this particular case is a matter of debate but as an overall point, I don't see anything wrong with getting help as needed from a family member, even if it wouldn't be the best thing to do if you were physically healthy overall.
Also my condition is an invisible one that people can't "see" unless they have some experience with it (certain physical traits experts in the disorder can see just looking at you). I also have a learning disability it took me three years of explaining for them to comprehend. It involves math and only math, the manger who dislikes me, thought I couldn't read.
To most people I interact with, LD= stupid. Not all of my managers have been like this, three treated me like a human being and understood the problems I was having (no gnashing of teeth when I had appointments, didn't talk to me like I was 5, etc). But they ended up leaving due to the female dogs (one was fired since he wouldn't give in to a SS customer (SS wanted him to break company policy), one went/was sent to another department since the FDs did not like her, and the other got transferred to another store out of the blue).
I would gladly leave the company and have another job, if another job was out there. I have a learning disabilty (Dyscalculia) so I cannot do any job that requires handling money or doing measurments, I have been searching for a tech school/college that I can get into that doens't require math (in our state you have to take and pass a test before entering college, I can't pass the math portion). The physical condition: no military, police, construction, etc.
I also have issues with my blood pressure/autonomic nervous system so that I times I am struggling to not pass out / escape mental fog and that is another reason my dad went to the boss.
The only accommodation I can get from DARS (Department of rehabilitation) is a person shadowing me, I am already treated like an idot, don't need to give them more ammo.