Whether a person convicted while suffering from severe mental impairment can invoke the Sixth Amendment right to know the nature and cause of the action against them based on their incapacity to know

QUESTION(S) PRESENTED 1) Under the Sixth Amendment right to know the nature and the cause of the action against a person, can a person convicted while suffering from severe mental impairment invoke that right based on the fact that he was incapable of knowing? 2) Does the above-described action also violate said persons Fifth Amendment right to due process, especially if the party was coerced into giving a false guilty plea?