Two other possible locations to obtain this information would be his application for a Soldier's pension, or that of his wife's, if either applied. Most likely he would have
disclosed the reason for his discharge therein. Confederate pensions were provided in the state of residence on date of application.
The other long shot would be if he was enumerated by mistake in the 1890 Federal Veteran's Census. On the enumeration sheets there is a box to describe war medical problems. I checked and did not find him there.