mentally sound

On the other hand, if you get a “general” power of attorney that only remains in effect while you’re mentally sound.

Just last week, broadcaster Esther Rantzen, who is terminally ill with lung cancer, begged MPs to attend a debate on a petition which argues that "terminally ill people who are mentally sound and near the end of their lives should not suffer unbearably against their will".

The petition being debated in Parliament urges the government to give MPs a vote on the subject and argues that "terminally ill people who are mentally sound and near the end of their lives should not suffer unbearably against their will".

It’s clearly nonsense, “not mentally sound,” and “lacks reason.”

According to the Merriam-Webster dictionary, the word crazy means “not mentally sound: marked by thought or action that lacks reason.”