THINGS THAT MAKE YOU GO HUH??

Kay, I know it happens to everyone cuz it can't be just me!  Things that make you scratch your head and go, "huh"?
You know what I'm talking about.....you're finished pouring milk in your cereal and you put the milk in the cupboard?  You go upstairs to get nail clippers, get up there only to stand at the top of the stairs and completely forget why you went up there to begin with?
Why?  I would love to know exactly what is happening to our brains at that very moment. 
Where does our brain go, when we're driving down the highway and all of a sudden we "wake up"  and realize we've been driving for the past 10 minutes without even realizing we were driving.  Your first thought is...did I miss my exit?  What was I doing?
We've all done it.  But.....why?
Why do we all go to the fridge to find something to eat, stand there and stare, shut the fridge only to return to do the same thing 2 minutes later?

What is going on in our brains when we can't remember something and it's "on the tip of our tongues"?  Or, when we write a word that we have written a thousand times and for some odd reason, it looks wrong.
I've heard of people who have thrown their left over dinner in the sink and their plate in the compost!  LOL.  Seriously...what is happening?

Some people call it "brain farts" others call it a "blonde moment".  I say "what the hell is going on in my brain?"