I missed Kaddish. I forgot!?

Yesterday was Sunday.  A day I don't have a strict routine.  I did family chores in the morning after morning services.   I had lunch, paid some bills, made some phone calls, worked on my lesson plans (have I said I'm a teacher?), then began making dinner.  Okay, the TV was on, a basketball game that I watched from time to time.  All of a sudden I remember: "Oh my God, shul!" I looked at the clock.  It was after 6:00 p.m.  I'd missed Mincha.  Fortunately, I was able to make the late Ma'ariv (evening prayer) service so I didn't miss both kaddishes.  But truth be told, I was mortified.  How could I forget to go to shul?  Isn't this obligation the most important facet of my life at present?  Am I not taking my kaddish obligation seriously enough? Or do I inwardly resent this burden of saying kaddish every single day, three times a day?  Or did I just "space out?" I'm only human.  I forgot.  Still, these questions are difficult to dismiss with an "oops." There's more than a grain of truth in all of them.