Reading bkeich's post reminded me that I recalled something about Alexander and WWI gas warfare. A quick check of Wikipedia confirmed this. From Wikipedia:
Alexander spent most of the 1918 season in France as a sergeant with the 342nd Field Artillery Regiment, 89th Division. While he was serving in France, he was exposed to German mustard gas and a shell exploded near him, causing partial hearing loss and triggering the onset of epilepsy. Alexander returned to the United States in April 1919 on the SS Rochambeau.[15] Following his return from the war, Alexander suffered from shell shock and was plagued with epileptic seizures, which people often misinterpreted as a sign of drunkenness; this only exacerbated his drinking problem.
Clearly, he was not the same after his time in the Army., although he lead the league in ERA in 1919 and 1920.
Link to Wikipedia on Grover Cleveland Alexander