I saw a counsellor earlier in the year (diagnosed with PND) after yelling at DD1 a lot. The counsellor told me that the important thing when you lose the plot with kids is the repair. So as long as you spend more time on the kisses and cuddles and tell them you are sorry then the yelling is not the thing that they will remember.
This - and also, once apologies have been made, move on. Tomorrow is a new day - don't keep talking about it. I'm not suggesting that you would, but I've found with my kids that it's important not to keep reminding them of the incident, even though you may still feel guilty for a while.