I have episodes exactly like this, but don't really have any diagnosis right now other than muscle weakness. Here's a fancy word for you to forget during these times: Anomic Aphasia. I think it can be caused by many different things. A friend of mine gets it really bad whenever her thyroid numbers are off.

Here's something to consider, though. Huperzine A is an acetylcholinesterase inhibitor, and it is being investigated as a treatment for Alzheimer's. There does seem to be a connection between acetylcholine and brain function.