Need some advice.

So I've been a little sidetracked the past week or two trying to get over the crud I can't seem to shake, so when V started feeling kind of down I figured it was the same thing.
The thing is that he seems to be fine a large portion of the day, then right in the middle of whatever activity he's involved in, he has to lay down. We didn't really make too much of it at first but then we noticed that he seems to be doing it more often, and at inappropriate times. Right in the middle of playing he will simply stop, lay on the floor, and stay there for several minutes. Sometimes he will nap a little after, but mostly he gets back up and goes about his play when he's ready.
His GI doc noticed the behavior at Mondays visit and urged us to go to our pediatrician.
When we arrived in the office, to be honest I was kind of afraid we were making too much of it. I mean when he's up, he's fine.
The whole wait time in the office he wouldn't settle down. I started to feel like I was just wasting her time. I strapped him into the stroller and gave him a book which he busily started working through the pages of when I noticed he was very quiet.
I looked over and his head was down on his shoulder, his lips had gone very pale, and he was not moving AT ALL.
I reached over and brushed his cheek and he looked at me and smiled. Then he layed his head back down again. A few minutes later he was back up and running.

WTH???

Dr. R went through all the "episodes" with me and the symptoms he has. She was initially worried about seizures, but he never goes limp or spaces out. He purposefully lays down and he will make eye contact. He doesn't go limp or spastic at all.
When I assured her of this she began leaning toward the possibiity of a cardiac arrhythmia. It would explain why he is so seemingly fine one minute, then down the next. Arrhythmias can cause a sudden feeling of weakness and dizziness. It would account for his need to lie down for several minutes at a time.

UGH...

We had to put off the bloodwork until tomorrow, but she wrote for a bunch. She thinks that if it were related to a deficiency in his counts though, that he would feel like that all the time and he definitely doesn't. It's weird.
We have tons of experience dealing with heart failure and such but this is uncharted territory.
Dr.R is going to set him an appointment with a neurologist just to be safe, and cardiology to check on the possible arrhythmia.
I'm just wasted tonight. Every time things seem like they're smoothing out he gets hit with something new.

Has anyone dealt with this type of issue with their children?