What those two verses are doing

We have certainly created man in the best of moulds. It gets used as a verse about bodies. The very next line continues, then We reduced him to the lowest of the low, and the passage is about moral state rather than appearance. Anybody who knows the surah will notice, and a course that pretends otherwise has lost them.

In the remembrance of Allah hearts find rest. That is true. It is also used to mean that if you were properly religious you would not feel bad, which turns a promise into an accusation. Ya'qub, peace be upon him, grieved until his eyes went white, and the Qur'an reports it without a word of rebuke.

Neither verse says that a believer who feels flat has failed at something.