The 38-year-old went from getting stuck into a training session last Wednesday to finding himself strapped to a ECG monitor on Sunday morning.
All clears have been given now though and Merris is ready to continue playing his part in steadying the stuttering heartbeat of Boro's season.
"It was a bit worrying, but everything is OK, which is the main thing. After it all they have discovered that I do have a heart," he joked.
"At training on Wednesday I started upping the tempo a bit when I felt a few chest pains and things tightened up.
"When I stopped exercising it all died down, but when it came to Saturday's game it was decided that I shouldn't be risked.
"On Saturday I rang up for an out-of-hours appointment to get myself checked out. They asked me a load of questions and then told me that they were going to send an ambulance for me.
"This was a bit of a shock, but in the end they went from that to highly recommending that I should go to A&E straight away to get checked out. That meant that I had to go in at 1am on Sunday morning.
"I had an ECG, they took bloods and I was asked questions by a nurse, doctor and a consultant.
"If your heart rate drops below 50 then they usually get you ready for resus and my resting heart rate was was 39.
"They asked me if I did any exercise and I told them that I do a little bit.
"After waiting for the results, nothing came up and they put it down to a virus that I'd had a week or so earlier. I can remember feeling a bit rough on the Sunday after the Gainsborough game, so it must have been then."
Merris also missed Tuesday's League Cup game at Farsley, but now he is feeling fit and ready to go once again.
He added: "I wasn't played on Tuesday, but I did a bit of warm-up work before the game and I came through that with no problems.
"I've been given the all clear now and I'm ready to go, I've also realised again that I don't like sitting in the stand and watching games.
"It is a frustrating time on the pitch at the moment, we've lost the last two in the league and one in the cup, but this is not a time for anyone to start panicking.
"In games it has just been down to making the wrong decisions. When we should be playing the right pass or delivering that cross, we have done something else.
"We have to strip it back and start doing the basics right.
"It isn't even Christmas yet, so there is so much football to play. We are addressing things now so we can start to push on once again.
"It isn't as though we are slip-sliding away because there are plenty of games for us, on Saturday we have the chance to get things going at home against Hyde.
"We will have the fans behind us and a good surface to play on, so there is no reason why we can't do just that."