To moan and sigh without being ill is the mark of empty, affected writing.
Tips
usage
Always in 呻吟 (to moan / groan). The idiom 无病呻吟 - 'moaning without being sick' - criticizes art or writing that fakes deep emotion it doesn't really feel.
register
The 'to chant / recite' sense is literary and archaic. In modern Chinese 呻 survives almost only in 呻吟 (to moan / groan).
Mouth radical on the left, 口. It marks a sound made by the mouth - here a low moan of pain. Same family as 吟 to chant (its partner in 呻吟), 叹 to sigh, 喊 to shout.