If you cast suggestion on somebody, and succeed, are they aware that you specifically cast the spell on them after it ends? Are they aware that they were under the influence of a spell at all? Yes and yes

— Mike Mearls (@mikemearls) March 26, 2018

it takes much more powerful magic to alter memories. magic provides a quick and dirty solution

— Mike Mearls (@mikemearls) March 26, 2018