Slurred speech, without an obvious cause, is really a reason to head for the ER. Don't pass go. Do not collect two hundred dollars. Don't go to work. Forget about the trip to Wal-Mart and the movie.
You have a "priority one" emergency.
As drnee pointed out there are numerous possibilities.
In a "worse-case" scenario you have a problem that might result in loss of brain function of paralysis if not diagnosed immediately. This not likely, but possible.
Go to an ER!
If you haven't taken any medication that is supposed to make you tired and you haven't been drinking alcohol: Go to the ER in case you are experiencing a stroke! Call 9-1-1.
Welcome to the MedHelp forum!
Extreme tiredness, high fever, hypoglycemia or low blood sugar, high blood sugar, kidney problems causing brain fog, liver problems causing brain fog, low electrolytes, brain lesions, very high blood pressure, alcohol or drug intoxication, etc can all cause slurred speech with tiredness. Basilar migraine, complicated migraine, Parkinson’s disease, transient ischemic attacks, hyperthyroid states, and seizures should all be investigated for. Please do not ignore this and consult a doctor ASAP or maybe go to the ER. It is difficult to comment beyond this without examining. A comprehensive investigation is required keeping all the points in mind.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!