Are you on any meds? They can cause "confusion" or slowness coming up with the correct word/pronounciation. If you aren't on meds I'd still go to the doctor and get a checkup, make sure there aren't any physical problems. There's a bit of use-it-or-lose-it but usually not for years? I think the "suddenness" of this change sounds like it might be a physical/hormone/chemical thing. Have you changed your eating habits, drinking more/less, different or more stress, etc.?