Apparent loss of vocabulary
For the last two years or so, I've found that I would run into situations on a daily (maybe even hourly) basis where I would be talking or writing, and I would suddenly come to seemingly random words that I could not recall. This makes speaking in complete sentences extremely hard, and makes writing a slow and painful task. These words are often common words or even expressions which I have used regularly in the past, and are apparently becoming lost to me. I find that I must visit the thesaurus more and more now.
Is this normal, or is this something that I should be concerned about?