I think having a card that explains what's going on will help you. If only so that people don't call an ambulance. I used to carry one because if my knee got bumped I could pass out. And more than that, had to take a few minutes to get the pain under control. EMTs couldn't do anything, and neither could the ER, so calling wasn't helpful. Having a card to hand to someone with some quick information and instructions on what they could do to help (a glass of water, something to grip, bring my purse, etc.) and things that wouldn't help (calling the ambulance, trying to get me to my feet). It definitely helped.
I think it's worth warning the kids too. Just a head's up so that they don't get scared. Stuttering is fine, but if it was a change from normal, I'd be concerned you were having a stroke.
And don't underestimate the ability to teach an entire lesson by writing on the board. Or, see if you can assign a student to lead part of the class for a short while. When I was a TA, I had a bad pain day very unexpectedly. After running out of the classroom (okay, wheeling as fast as I could) to throw up (pain reaction) I had the students work in small groups to formulate solutions to the problems we were working on, and then present them. It worked so well, we did it more frequently after that.