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."

DSI Plumbing and Heating Ltd of Hampshire was also ordered to pay £1,000 costs at Bournemouth Crown Court after admitting two breaches of the Health and Safety at Work Act 1974.
Faults were found at 309 properties in Poole and 40 flats in Reading.
Homes in Harbour Reach, Poole, were evacuated following a gas leak in 2009.
The court heard that a Health and Safety Executive (HSE) investigation found that between 2005 and 2007 flues and gas supply pipes had not been properly fitted in the new development.
Two self-employed men who worked for the company, Robert Percival, 49, of Legion Road, Poole, and Andrew Church, 42, of Ensign Drive, Gosport, both pleaded guilty to a single breach of the same legislation.
Percival admitted commissioning a gas installation at one property between June 2007 and April 2008 and Church admitted making false entries into documents, which he completed without carrying out the required checks between January 2006 and March 2007.
They were both given a two year conditional discharge and were each ordered to pay costs of £250.
HSE's head of operations, Harvey Wild said the faults, found in more than 90% of Harbour Reach and two thirds of the Caversham Road development, were only discovered after residents complained about ill-health.
He called the breaches "serious failings" after the sentencing and said: "It is fortunate that in this case, no-one suffered long term ill-effects but the consequences of the faults, if left undetected, could have been fatal.
"Gas installers need to make sure flues and pipes can be properly checked and all installations are checked for safety as part of commissioning to ensure lives are not put at risk."
Essex off-spinner Simon Harmer says he is "riding the wave" after taking 14 wickets in both of his past two County Championship matches.
[NEXT_CONCEPT]
A heating firm has been fined £10,000 after faulty gas installations were discovered in more than 300 properties across Dorset and Berkshire.