Mental illness on a soldier's service papers - how severe?

[Will O'Brien]

Although I have little to contribute, I must say that I have found this thread fascinating. In relation to why such a man would have been accepted for service in 1917, despite previously being rejected, I wonder whether he showed some willingness or desire to serve. Whilst this is a poor reason for the army to enroll him it could be a possible explanation as to how he managed first to be accepted & then proceed through the training phase to the front line.

[Neale1961]

Since your French soldier died young, I wonder if his death certificate would give you any more information about his medical / mental condition?