"Interviewer was grinding me down this morning". But if I had to say it in a manner like "I had to go through a lot of grinding in the interview" would it be correct? (without the word 'down' because the phrase is 'grind down'). Or would only 'grinding' here without 'down' would imply something DANCE related? (which isn't what I mean here obviously)
I'm sure you understand that whichever of these you choose it will be a metaphorical use of the term 'grinding'.
'Grind' is a verb with a physical meaning of which I feel sure you are aware. 'Grinding down' is an idiomatic expression used for people and situations that tend to mentally exhaust one. 'Work grinds me down'.
'Grinding' on its own is less commonly used metaphorically, but that does not mean it is impossible to coin phrases which contain it.
'The daily grind' is an expression of hopelessness and the inevitability of work and its attendant miseries.