Many "moments".
A very near miss with an overtaking Jaguar whilst flying a Puma at very low level; the sky went very briefly dark as it overflew us. We only saw it as it appeared from our 6 o'clock to our twelve o'clock. Not only did we hear it but at the same time its down-wash hit us and we smelled its exhaust fumes. There must have been about ten metres of (vertical only) separation.
A more recent one: Flying a civvie helicopter in solid IMC and in torrential rain over mountainous terrain, knowing that the extensive cloud extended well below "deck" level below us (down to 300' amsl as it turned out at the coast) when the amber flashers and tail rotor chip light illuminated. The checklist drills (operating the "fuzz burner" switch) didn't make it go out. There were no other symptoms of an impending tail rotor gearbox failure so the only option was to carry on and hope it was a spurious caption. Thankfully, it was and it went out all by itself (water ingress into the connecting plug). But anyway, it caused a very worrying few minutes.