Sounds a bit like Atrial fibrillation? My mother used to have this but it has settled a bit in recent years. See your GP for a cardiologist referral.
It sounds nothing like AF and it would show on both ECG and echo.
OP
Sorry I'm a bit late to this.
Not sure what you know about your heart and circulation so I'm going to start with a really basic concept.
Your circulation system is like your central heating system, the pump (boiler or heart) sends fluid round the system.
It has both mechanical and physical parts.
The ECG shows the electrical system, the echo the mechanical function.
You have had a normal echo so the structures are all normal.
Palpitations are just heart beats that you can feel, some people feel them a lot and some people don't. It's a bit like looking at your inner arms, on some people you can see veins, on others you can't but they are still there.
As you mostly get them lying down there is a fair chance that you just feel them because of the position you are in.
Does your heart rate increase when you have these palpitations? If it does then it could, and I repeat could, not diagnosing you here be an SVT. If it is then there are a couple of ways to get rid of it. Some need a medical professional and for yuo to be in hospital.
One that doesn't and won't cause a problem if it isn't is ice cream.
As big a chunk of ice cream as you can manage to swallow in one.
Another that works in children is to rub an ice cube on your nose - I know it sounds like I am having a joke, I'm not.
If your heart rate slows down when you get your palpitations then it is possible that what you are feeling is the effect of the beta blockers.
Beta blockers don't just slow your heart rate, they increase the 'squeeze' of the heart, so the pump is sending out more liquid with each squeeze.
Keep a journal of when they occur to see if there are any patterns. Learn to take your pulse and do that when you have any palpitations, keep a record of it, but also of your normal pulse.
Monitor if you have eaten, or had caffeine.
At least then you can go to your GP with a record of what has been happening.
When you see the cardiologist ask about a 'cardio memo', there are various other names for them but it is similar to a 24 hour ECG but instead of being wired up all the time you put the monitor to your chest and record when you have symptoms, you normally have one for about 2-4 weeks at a time.
susurration
Thant sounds like an ablation.
OP if it is SVT and you are symptomatic the cardiologist may suggest this procedure. You basically go in to hospital, the cardiologist puts wires in your groin up to your heart (you will have anesthetic) and freezes or burns a tiny bit of the electrical system away.
good luck