The title says it all. What can feel like palpitations? I have an interesting story you might wanna read.
So.. i used to get 0 palpitations a day, until last week.
Since last week i have been feeling some weird heaviness / flutter / "elevator" / sink feeling in my chest and troath. A quick google search and some of my basic knowledge about how the heart works confirmed it: PVCs (Premature Ventricular Complexes), or Palpitations, for people who call them like this.
Obviously I was concerned, because I didn't experience this until then, but I said: "Everyone gets those, right? F*ck it, it is what it is"
The next day it happens again, and the next day again... and again... and uh-oh.. something is off.

So I went to a cardiologist to check it out because obviously it was something new.. I don't smoke or stuff like this so what can cause them.
The cardiologist makes me lay down so she can perform an ECG. I say to myself "It would be a shame if they will say everything is normal.. right?" And just when i thought about that i felt it. A "SKIPPED BEAT FLUTTER ELEVATOR HEAVINESS IN CHEST AND TROATH FEELING". It was a PVC.. HOORAY, right? Well.. no. 

When the ECG was done she looked over it and I was waiting happily.. i said: "So.. that's what I'm talking about.. is it dangerous?" She looks at me and says: "What do you mean?", and she hands me the ECG... i couldn't believe my eyes! The PVC was NOT there! It was just Normal Sinus Rhythm. How can this be? Like i felt the skipped beat flutter devilish scary thing!!!! Wheres the pvc?!?

Next thing: echocardiogram. I said to myself: "Okay.. that was weird, i will ask her when this en-" and just when i was about to finish my sentance.. again. I felt that scary thing again. I asked her: "Did you see it?? On the monitor??" She said she did not see any abnormality of the rhythm, nor the heart itself, it appeared clean and healthy.
Of course I was mad! I was clearly having palpitations! 

I asked her about it, and she says that maybe it's just in my brain or not heart related, since it doesn't appear on the ECG, nor the Echocardiogram. I will go with the second option, "not heart related", since it's not just in my head! What can mimic a palpitation, please reddit! Help me :(.
Context: I would usually feel those things when I am: Sitting down after exercise, laying down, sleeping on my left side, or sitting for a long time. Since they are not palpitations, what are they? Something neck related?
Thanks!