Why have the US military authorities not allowed an independent assessment of the accused / prisoner physical and mental health? I assume that there is such a person, is this not an Inspector General's role?

Instead it appears that his treatment is far from proper care and custody. Which gives some cause for concern and the clear possibility of an "own goal".

Then one must acknowledge that in the USA, especially in Federal cases, the threat of and use of pre-trial detention is used to undermine the accused's wish for a full trial.