I knew it was a part of the "bigger problem" years ago, but I had been able to cover it up, dismiss it, blame it on stress or rushing, and just laugh it off. Not anymore. The day my youngest son stopped dead in his tracks as he was helping me pick up and straighten things in the dining room, it became very real. I was giving him instructions and I told him to, "Put the books on the table." He froze and looked at me, eyes wide, and exclaimed, "Mom!" I asked him what was wrong and he said, "You told me to put the books on the ceiling!" "What? I did not, I said 'table'." I had no recollection of saying 'ceiling' instead of 'table'. But that doesn't mean I didn't.
Sometimes I catch myself substituting the wrong word, but sometimes I don't even notice, until I get a reaction similar to my son's...or when the other person I'm having a conversation with gives me "the look", and then I know I've done it again.
Other difficulties I have with speech that come and go include halting, hesitating, or scanning speech, slurring, or not being able to "find" the word that I want to say, using "words" that are not even a part of the English language, or problems with getting any of the words I know I want to say to come out at all.
It can make me feel self-conscious, embarrassed, but most of all, very frustrated. I was valedictorian of my class, for goodness sake! But it can make me sound like an uneducated, bumbling, gibberish-talking woman who has had a little too much alcohol to drink. So please, don't "assume" anything if you hear me or another person experiencing these problems with speech and language. There just might be a real reason and explanation for it, and it's nothing we can control.