I wouldnt beat yourself up to bad about it. First of all your not feeling well and getting children ready in the morning is hard enough and even harder when they are not cooperating. Its normal to snap at your kids now and then just as long as you dont go overboard and to me it does not sound like you did.
When I yell at my kids and feel guilty afterwards I usually will try to talk to them about it. I will apologize if I was out of line. If it was something that I feel was justified on my part I will still talk to them and let them know what actions need to be changed.

Take care and like I said, dont beat youself up about it too much.