Lethologica (lee-tho-LO-gi-ca) —
the inability to remember the right word; a psychological disorder that inhibits an individual's ability to articulate thoughts by temporarily forgetting key words, phrases, or names in conversation
Letho- from the Ancient Greek, Lethes, a river of Hades that effaced memories, and logica from the Greek word for word, logikos.
In daily conversation, I often suffer from Lethologica. I think this is why, for the most part, I prefer to write.