Fall down and Nose-dive

Fall down verb - Lose an upright position suddenly.

Nose-dive and fall down are semantically related. In some cases you can use "Nose-dive" instead a verb "Fall down".

Nose-dive verb - To go to a lower level especially abruptly.

Fall down and nose-dive are semantically related. Sometimes you can use "Fall down" instead a verb phrase "Nose-dive".