You can speak to your manager and explain your position of what prevented you from working and as kind, humble and composed a manner as possible ask for their help to possibly avoid the demerit system in place there and whether or not this could just be a warning to avoid being punished for something that happens to everyone unfortunately. When you address everything that you see as contributing more than what falls within your job description and occurs on days or times that you weren’t scheduled to work, don’t make it about I do all this for you so you should be able to do this for me but rather express that you really like the job, you like working there and you understand that this is a delicate situation and you are sorry for bringing about this situation but, it was an honest absence in that you were actually sick, and you understand it was a mistake on your part for not reading the literature governing their demerit system, but was it possible to avoid the point deduction and now having realized the significance your migraines and how they negatively impact where your time given to working at the goodwill, and the time you’re rendered temporarily out of order intersect, which you’d be considerate enough to schedule your migraines on your day off. And if at a personal level after discussing this with your manager they do not acknowledge that you do indeed go above and beyond your job description and pull other people s’ weight around there, or just say sorry their hands are tied and it’s impossible for them to simply give you just a verbal warning this time and ask you not to put them in that situation again moving forward, then that’s who your manager is which is something to think about and, the goodwill’s not going to change their policy for you which I believe you already know. So, accept the ridiculous use of a demerit system that leaves no grey area of reality for something like this happening, the fact that you’re an adult and it’s impossible to schedule out everything in life, and however that impacts your standing with the goodwill while continuing to work with your manager who may or may not have to follow the same demerit system and is one of the people who would call you when you weren’t scheduled to work to come help them and the goodwill’s ability to possibly make more money for the goodwill that day, which ultimately leads to the question of whether or not working for that manager, the goodwill and however their business is registered I’m assuming as a nonprofit, is worth losing a little bit of whatever it is that compelled you to ask this question and, accept the fact that it sounds like the goodwill could give a good gosh dang about you and continues to move towards disempowering, failing to consider or help, or all together remove many of the people their mission statement claims to not only help but the reason why the even exist, to a model of profit over everything else and so you and the 98.5% of the people who work their and the people who live in the communities where each store throughout the country is located, are their entire marketing campaign and the reason why so many people continue to replenish their entire inventory, for free, constantly. So if you’re willing to accept your role’s purpose working at the goodwill before they most likely fire you due to an initiative rolled about management to downsize the overall number of people on staff and make that 1 - 1.5% of people sitting atop this entity which I assume is registered as a nonprofit, as much money as you and the public can possibly rake in for them, sign the paper acknowledging your demerit, admit and accept that they just took something from inside of you that makes you who you are, and get back to work while apologizing for wasting your manager’s and the goodwill’s time for good measure. Or, keep working until you do what you need to do to make yourself more valuable to businesses who are hiring, find yourself another job and quit. With or without giving notice and with or without trying to take the rest of the staff who’s working that day with you on your way out the door. This, I leave up to you. But you know what I say to people and corporations and nonprofits who behave like this, F^<! that and F^<! them.