I, too hate this one the most.
It makes me feel insignificant and useless to anyone else. I used to be able to speak in front of people clear and concise. I used to be able to train people easily, I was a good teacher. I understood things, I was a quick learner and good student.
Now I am just a big dope. It takes me seconds to process things that should be instant and hours to process things that should take minutes. I look at my 5th grade son's homework and my eyes start swimming and my brain starts doing the hokey pokey.

I hate feeling stupid and I really hate trying to cover that and keep people thinking I'm still smart. I say way too often, "**incoherent string of syllables, deep breath**I'm sorry. I'm not stupid, I swear..."
I think the worst part, which just happened to me this moring, is the people watching you, waitig for you to figure out what you are saying so they can figure it out. In front of my husband and a property manager this moring I was only trying to ask how long the waiting list was. It didn't come out that way, I tripped over my words, I'm pretty sure I made up a few words and threw in a "you know, the...thingies?" at the end. My hsband and the woman just sat there patiently watching me in silence as I got more flustered. How many times do you end these conversations with "Oh, just forget it..."