conflict with father

I have ADHD. I know that this is a web site for marriages but I have a different kind of relationship problem.  I seem to always have this underlying conflict with my dad.  I'm not sure why.  Yesterday I had a "blow out" yelling argument with him in a parking lot.  We both left if a hurried "huff" with slamming car doors.  The content of the argument is not all that important.  It involved the way he talked to one of my children.  I didn't approve and said, "Dad, that's enough".  He stayed and helped me put the kids in the car then handed me my bag without a word and started to leave.  I should have let it go but I didn't have enough strength to control myself.  I asked if he was mad at me.  He said, "No", then mumbled as he always does, half sarcastically, "I just never say the right thing so I should just keep my mouth shut".  In my own stupid uncontrolled way, I said, "What is wrong, why are you always saying that, I appreciate everything you do".  He said he didn't want to get into an argument.  I responded angrily, "fine, then I'm going to go home and not feel guilty".  He said he didn't want me to feel guilty.  I told him that I always do when things like this happen...From there, it exploded and phrases like "you will respect me because I am your 75 year old father" started flying.  I was just trying to defend my child and myself but I do it in a very unhealthy way. 

Needless to say, I haven't been able to function since.  I was up late last night and I'm just walking in circles today.  I'm trying to do the right thing but my brain won't let me get past it to even rationally apologize.  I'm having a hard time even taking care of my children today.  I have so much work to do but all I do is cry.  I am angry, sad, guilt ridden, physically nauseous, and dysfunctional all around.  Any advice from someone who doesn't have ADHD but may have a similar issue.  I'm open to opinions as to the "right thing to do" and will not be offended by anything.  I'm trying so hard to get better.  Please help.