Oh hun, lol I only have ONE and I do the same thing sometimes!! And yes, it makes me feel sooo awful to see the look on her face afterwards, but the great thing about littlies is how forgiving they are...
Don't stress too much hun, we all have our bad days, it can be so hard being at home with the kids all the time. We're not perfect, nor are the kids, so just give the little one a hug and tell him you're sorry (but add that he was being naughty), he will forgive and forget in no time at all. I really don't think that little incidents like this will affect your kids long-term, my God I remember my mother screaming her head off at me and my brother CONSTANTLY when we were kids and yet we still love her and know that the good days far outweigh the bad days (and that usually, the bad days had a lot to do with us acting out and being little t*rds!). Read him a story or pop on a DVD, or do whatever fun thing you like to do together, I can almost guarantee you he'll entirely forget about it in a few minutes

*hugs* hope you're feeling better. I know none of us here are judging you, we all have our moments