TexasRanger, given your difficulties speaking, you may want to have a couple of "Medical Emergency" flashcards with appropriate phrasing that you can use when speaking is difficult.
Eg - "I am having a migraine. I cannot "just take a pill". I need to leave to see my doctor immediately. Not doing so could have life-threatening consequences."
Consult with your doctor, etc, on appropriate phrases. It might also help to have a few "standard customer inquiries" on similar cards. Other e-hellions could come up with suitable phrases.
Blarg and delabela also had some very good points about this.
Also, the classic advice in this situation - document , document, document! Keep it "just the facts, ma'am". eg On xx/xx/xx date, I developed a migrain while at work, starting at xx time, leaving me unable to continue my duties. BadManager refused to let me see the doctor, just saying "take a pill". My migraine worsened over the next half an hour, and at xx time I had to be taken to the emergency department of xx hospital by ambulance. I was informed by Dr X that the delay in seeking treatment could have been fatal.
Also document your attempts to see manager, HR, etc.
Could other ehellions with work experience help out with phrasing?
Silliness follows - DON"T do this for real!!
Evil Armada thinks that when Bad Manager pulls a "no you can't have that shift off" or "take a pill", act a bit stupid - and cry, in public! "I need to go to the Doctor! If I don't go to the Doctor I could DIE!!! Why are you trying to KIIIILLLL MEEEE?
Have a big melodramatic breakdown, very publically, in front of a large group of customers.
Like Allee Brosh, in The Party http://hyperboleandahalf.blogspot.com.au/2010/09/party.html