His career-best 9-95 helped Essex beat Middlesex by an innings and 34 runs.
"You can't really put it into words. Sometimes things go your way," the 28-year-old South African told BBC Essex.
"I was saying to our scorer I'll probably never take four five-fers or 28 wickets in two games ever again - it's just been one of those weeks."
He continued: "You've got to ride the wave while you can because I can guarantee you I'll be back in South Africa at the Wanderers, bowling on an absolute road and getting smashed all over the place."
The victory over the reigning champions left Essex 29 points clear at the top of Division One in their first season back in the top flight.
Kolpak player Harmer, who returned career-best figures of 14-128 in last week's win over Warwickshire, has now taken 47 wickets in eight matches this season.
And he said a Championship day-night trial with the new pink ball helped his cause against Middlesex in Chelmsford.
Harmer said: "I think everybody's feedback was that it came off the bat a bit better and there was a bit of extra bounce, and obviously being a spinner on day four when the wicket's slow and low to get that extra bounce is nice.
"It keeps the batsman guessing because it takes the sweep shot out of the equation because it's bouncing.
"They need to look to then play off the back foot or whatever, so it definitely helped me."
Essex off-spinner Simon Harmer says he is "riding the wave" after taking 14 wickets in both of his past two County Championship matches.